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>>

ARISTOTLE AND THE SCIENCE
OF NATURE


Andrea Falcon™s work is guided by the exegetical ideal of recreating
the mind of Aristotle and his distinctive conception of the theoretical
enterprise. In this concise exploration of the signi¬cance of the
celestial world for Aristotle™s science of nature, Falcon investigates
the source of discontinuity between celestial and sublunary natures
and argues that the conviction that the natural world exhibits unity
without uniformity is the ultimate reason for Aristotle™s claim that
the heavens are made of a special body, unique to them. This book
presents Aristotle as a totally engaged, systematic investigator whose
ultimate concern was to integrate his distinct investigations into a
coherent interpretation of the world we live in, all the while mindful
of human limitations to what can be known. Falcon reads in Aristotle
the ambition of an extraordinarily curious mind and the con¬dence
that that ambition has been largely ful¬lled.

a n d r e a f a l c o n is Assistant Professor in the Department of
Philosophy at Concordia University, Montreal. He is the author of
Corpi e movimenti: Il De caelo di Aristotele e la sua fortuna nel mondo
antico (2001).
ARISTOTLE AND THE
SCIENCE OF NATURE
Unity without Uniformity


ANDREA FALCON
cambridge university press
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo

Cambridge University Press
The Edinburgh Building, Cambridge cb2 2ru, UK
Published in the United States of America by Cambridge University Press, New York
www.cambridge.org
Information on this title: www.cambridge.org/9780521854399

© Jan Paulsson 2005


This publication is in copyright. Subject to statutory exception and to the provision of
relevant collective licensing agreements, no reproduction of any part may take place
without the written permission of Cambridge University Press.

First published in print format 2005

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Cambridge University Press has no responsibility for the persistence or accuracy of urls
for external or third-party internet websites referred to in this publication, and does not
guarantee that any content on such websites is, or will remain, accurate or appropriate.
In memory of
Mario Mignucci, my teacher, who cared
Lo duca e io per quel cammino ascoso
intrammo a ritornar nel chiaro mondo;
e sanza cura aver d™alcun riposo,
`
salimmo su, el primo e io secondo,
tanto ch™i™ vidi de le cose belle
che porta ™l ciel, per un pertugio tondo.
E quindi uscimmo a riveder le stelle.
Contents




Preface page ix
Acknowledgments xiii
List of abbreviations and conventions xv

The unity, structure, and boundaries of Aristotle™s science
1
of nature 1
Bodies
2 31
Motions
3 55
The limits of Aristotle™s science of nature
4 85
Epilogue 113

Bibliography 122
Index of names 130
Index of passages 132
General index 138




vii
Preface




This book develops the investigation I began in Corpi e movimenti: il De
caelo di Aristotele e la sua fortuna nel mondo antico (Naples, 2001). There I
discussed Aristotle™s reasons for the view that the celestial bodies are made
of a special body which naturally performs circular motion and is differ-
ent from, and not reducible to, earth, water, air, and ¬re. I have also
shown that very few in antiquity, even within the school of Aristotle, were
prepared to accept this doctrine, though many, if not most of them,
shared Aristotle™s view that the celestial world is a special and somehow
distinct region of the natural world. This book incorporates material from
the Italian one but presents it in the light of a new project. By studying
the reception of the view that the heavens are made of a special body, I
have come to appreciate not only how unusual Aristotle™s conception of
the natural world is; I have also come to understand how this conception
may have affected the way Aristotle conceives of the science of nature.
This book is an attempt to explore the signi¬cance of the study of the
celestial bodies for Aristotle™s project of investigation of the natural world.
While Aristotle argues, against his predecessors, that the celestial world
is radically different from the sublunary world, he is not envisioning
two disconnected, or only loosely connected, worlds. On the contrary,
Aristotle conceives of the natural world as one department of reality with a
suf¬cient unity to be the object of a single science. I show, however, that
for Aristotle this world exhibits unity without uniformity. More speci¬-
cally, there are features of the celestial world that outrun the explanatory
resources developed by Aristotle for the study of the sublunary world.
According to Aristotle, there is an important discontinuity between the
celestial and the sublunary worlds, and this discontinuity leads him to a
further conclusion: that the celestial bodies are made of a special body,
unique to them.



ix
Preface
x
But there is more to this book than an attempt to understand the
reason that motivates Aristotle to endorse the view that the celestial bodies
are made of a material principle unique to them. On the interpretation I
am recommending, Aristotle is not only a systematic investigator of the
natural world, he is also modest in recognizing human limitations on the
extent of what can be known of this world. In the extant works, he is
engaged in the study of the natural world in all its aspects on the crucial
assumption that this world is a cosmos: that is, a structure that is intrinsic-
ally intelligible. But the study of this structure leads Aristotle to a certain
view of the natural world and the place that we occupy in it. As a result of
this view, Aristotle comes to think that what is intrinsically intelligible
does not collapse into what can be known by us. Put differently, there is a
lack of intelligibility to us in the natural world. I postpone discussion of
this lack of intelligibility until the ¬nal chapter of the book.
Chapter 1 introduces the reader to a number of structural features of
Aristotle™s science of nature and the question of its unity and its bound-
aries. In the opening lines of the Meteorology, Aristotle outlines a program
for the investigation of the natural world. I focus on this program and
show that Aristotle™s science of nature is structured in a certain way. I
argue that this structure is crucially dependent upon a certain conception
of the natural world. For Aristotle, the natural world is a causal system in
which the direction of the explanation is from the celestial to the sublun-
ary world only. A full appreciation of this conception of the natural world
will help the reader to understand the precise sense in which Aristotle™s
science of nature is a distinctly organized science. In this context, I argue
that the opening lines of the Meteorology reveal a ¬rm grasp of the
boundaries of the science of nature. Tellingly, the study of the soul is
not mentioned as part of the program of inquiry into nature. Elsewhere
Aristotle makes it abundantly clear that the study of the soul is prelimin-
ary to the study of life, but it is not a part of the science of nature. I discuss
the problematic relation between the science of nature and the study of
the soul and the unique status of the De anima within the Aristotelian
corpus.
Once the conceptual structure and the scope of Aristotle™s program for
the investigation of nature are in place, in subsequent chapters the reader
is introduced to Aristotle™s view that the student of nature is concerned
not only with natural bodies but also with the explanation of their
motions.
Chapter 2 discusses the signi¬cance of Aristotle™s emphasis on body in
the opening lines of the De caelo. A close analysis of Aristotle™s conception
Preface xi
of natural body reveals that this conception is much richer and more
complex than the concept of a three-dimensional object that occupies a
certain region of the natural world. To begin with, natural bodies are
divided into celestial and sublunary bodies. In the sublunary world,
Aristotle admits a further distinction between composite and simple
natural bodies. Finally, Aristotle develops a hierarchical conception of
natural bodies: the natural bodies are themselves composed of natural
bodies, and the simple bodies are the ultimate material principles of all
natural bodies, and as such they are the natural bodies par excellence. For
Aristotle, the natural world is the totality of the existing natural bodies.
Chapter 3 describes how and why Aristotle relates speci¬c bodies to
speci¬c motions. Since the bodies in question are natural bodies, it is no
surprise to discover that the explanation of their motions involves an
appeal to their nature. More directly, Aristotle is committed to the view
that motion is either natural or non-natural. I explore Aristotle™s doctrine
of natural motion and argue that he has left a coherent doctrine, even
though at times he expresses himself in a way that is far from being crystal
clear. I also study the way in which this doctrine is used to introduce the
thesis of the existence of a simple celestial body which naturally performs
circular motion. In this context, I suggest that celestial motion is not
merely the circular motion performed by the celestial simple body, and
that a full explanation of celestial motion requires an adequate psycho-
logical cause, namely a soul of a certain type. Finally, in the De natura
deorum, Cicero credits Aristotle with the following tri-partition: (i) nat-
ural motion, (ii) forced motion, (iii) voluntary motion. The great intrinsic
interest of this testimony, whose ultimate source presumably is Aristotle™s
lost dialogue On Philosophy, is the claim that celestial motion is a case of
voluntary motion. I explore the reason for this claim which clashes with
our basic intuitions about the voluntary.
Chapter 4 emphasizes Aristotle™s epistemological pessimism regarding
the possibility of knowledge of certain aspects of the celestial world.
Aristotle™s pessimism ultimately depends upon his conception of the
natural world. Aristotle believes in the existence of celestial and sublunary
natures, but he does not believe in the uniformity of nature. His con-
sidered view is that nature is not a uniform principle. I discuss the reasons
that might have led Aristotle to take this view as well as the consequences
following from this view for the study of the celestial world. In the extant
works, Aristotle is reluctant to engage in an investigation of the celestial
world when and where the lack of information at his disposal cannot be
overcome by an appeal to similarities which the celestial natures share
Preface
xii
with the sublunary natures. He also makes a considerable effort to square
the case of the celestial bodies with the conceptual resources developed
and re¬ned in the study of the sublunary world. But how successful is this
effort? I focus on celestial matter as a case study.
The Epilogue studies the language traditionally used to refer to the
celestial simple body introduced by Aristotle. Doxographers and com-
mentators refer to Aristotle™s celestial simple body as the ¬fth body, the
¬fth substance, the ¬fth element, the ¬fth nature, and even the ¬fth genus.
No one of these expressions is used by Aristotle, who refers to the celestial
simple body as the ¬rst element, the ¬rst body, or the ¬rst substance.
Aristotle mentions aither, but only as the traditional name for the upper
¯
part of the natural world. I argue that this language is further evidence
that Aristotle was fully aware of having arrived at a view of the natural
world which was not only controversial but in some important sense also
unique.
A ¬nal note on my language. I speak of natural world and natural
bodies instead of physical world and physical bodies because our concep-
tion of the physical does not do justice to the richness and complexity of
Aristotle™s ta physika. This richness and complexity will become apparent
in due course. For the time being, I am content to point out that we
routinely contrast the physical with the mental. This contrast is emphatic-
ally not shared by Aristotle. What we recognize as the mental is part of
Aristotle™s natural world, even if he seems to be prepared to admit that
what we recognize as the mind has the power to go beyond that which is
merely natural.1 For the very same reason, I prefer to speak of the science
of nature instead of physics.


1 This claim requires elaboration. I refer the reader to my discussion on the boundaries of the science
of nature in chapter 1, “The unity, structure, and boundaries of Aristotle™s science of nature.”
Acknowledgments




The idea of this study grew out of a research seminar on the De caelo that
Hendrik Lorenz and I conducted at Oriel College, Oxford, in the spring
of 1999. I wish to thank the friends who attended the seminar, and in
particular Michael Frede, David Charles, and Paolo Fait. The book was
written in the last four years. I owe a great deal to the people whom I had
the good fortune to know while visiting the Departments of Philosophy at
Berkeley, Ohio State University, and the University of Pittsburgh. How-
ever, the book came to fruition at Virginia Tech. I wish to express my
gratitude to the Department of Philosophy at Virginia Tech for providing
me with the ideal environment to ¬nish what was partially accomplished
elsewhere. I also bene¬ted from trying some of my ideas in different
contexts. Earlier versions of chapter 1 were presented at the Princeton
Colloquium in Classical Philosophy, December 2001, and at the Univer-
sity of Pittsburgh and the University of Toronto, in the winter of 2002. A
section of chapter 4 was read at the Berkeley Conference in Ancient
Philosophy and at the USC/Rutgers Conference in Ancient Philosophy,
in the fall of 2000. I am grateful to these audiences for their helpful and
sympathetic criticisms. My work has been facilitated by a four-year
research fellowship awarded by the University of Padua. I wish to express
my gratitude to Enrico Berti who provided me with the freedom I needed
to pursue my research.
I am most grateful to Alan Code, Michael Frede, Jim Lennox, and Bob
Sharples for reading earlier versions of this book and making constructive
comments, which I have tried to incorporate in the ¬nal draft. Of course
I am entirely responsible for any errors that may still remain in the
following pages. I would like to thank Charles Klopp who has translated
the epigraph from Dante™s Inferno for this book.
The friendship of Carol Price has sustained me during the past few
years. I thank her for this precious gift. She has successfully made me feel
at home away from home.
xiii
Acknowledgments
xiv
The love of Cristina has nurtured me, especially in the years that we
lived on different sides of the ocean.
This book is gratefully dedicated to Mario Mignucci. By his example
I have learned that reading Aristotle not only requires philosophical
acumen, together with a combination of philological and historical skills;
it also requires the dedication and courage of a mind open to the
enormous possibilities of a text which remains largely unparalleled.
Abbreviations and conventions




Frequently cited ancient titles are abbreviated as follows:
Alexander of Aphrodisias
DA De anima
In Metaph. In Aristotelis Metaphysica commentarium

Aristotle
A post. Analytica posteriora
Cat. Categoriae
DA De anima
DC De caelo
EE Ethica Eudemia
GA De generatione animalium
GC De generatione et corruptione
HA Historia animalium
IA De incessu animalium
Metaph. Metaphysica
Meteor. Meteorologica
NE Ethica Nicomachea
PA De partibus animalium
Phys. Physica
PN Parva naturalia
Rhet. Rhetorica
SE Sophistici elenchi
Top. Topica

Cicero
Acad. Academica
De ¬n. De ¬nibus bonorum et malorum
Nat. deor. De natura deorum


xv
List of abbreviations and conventions
xvi
Tusc. Tusculanae disputationes

[Galen]
Hist. philos. Historia philosopha

Hippocrates
VT De vetere medicina

Philoponus
Contra Aristotelem De aeternitate mundi. Contra Aristotelem
In DA In Aristotelis De anima commentaria
In GC In Aristotelis De generatione et corruptione
commentaria

Plato
Tim. Timaeus

Proclus
In Remp. In Platonis Rempublicam commentarii
In Tim. In Platonis Timaeum commentaria

Sextus Empiricus
M Adversus mathematicos
PH Pyrrhonei hypotyposes

Simplicius
In DC In Aristotelis De caelo commentaria
In Phys. In Aristotelis Physica commentaria

[Simplicius]
In DA In Aristotelis De anima commentaria

Stobaeus
Ecl. Eclogae

Strabo
Geo. Geographica
List of abbreviations and conventions xvii
Xenophon
Mem. Memorabilia

Other frequently cited titles are abbreviated as follows:
¨ ¨
Aetius, Placita (reconstruction in Diels, Dox. gr.)
Aetius
Arius Didymus, Epitome (fragments in Diels, Dox.
Arius Didymus
gr.).
DK H. Diels and W. Kranz, Die Fragmente der
Vorsokratiker, 3 vols. (Zurich, 19516 ).
¨
Dox. gr. Doxographi graeci, ed. H. Diels (Berlin, 1879).
LS A. A. Long and D. N. Sedley, The Hellenistic
Philosophers (Cambridge, 1987).
SVF J. von Arnim, Stoicorum veterum fragmenta, 3 vols.
(Leipzig, 1903“5); vol. iv Indexes, ed. M. Adler
(Leipzig, 1904).

In accordance with general editorial practice, words in < > indicate
addition to amplify translation. Where the author™s name appears in
square brackets it means that the work is generally regarded as not
genuine.
chapter 1

The unity, structure, and boundaries of Aristotle™s
science of nature



introduction
Asked to what end one should choose to live, Anaxagoras replied
“to study the heaven and the order of the whole cosmos” (Aristotle, EE
1216 a 12“14 ¼ DK 59 a 30).

Aristotle is not merely concerned with solving a list of problems or
discussing a certain number of topics. He is engaged in an ambitious
project of investigation. This project consists in an attempt to establish
the right sort of connections “ explanatory connections “ between the
things of the world. If this investigation is successful, it not only provides
us with knowledge, but it gives us understanding of the world. The
investigation of the natural world is no exception to this rule. Aristotle
has left a certain number of logoi, each of which is a relatively independent
and suf¬ciently self-contained argument devoted to a particular topic or
problem.1 But there is no doubt that these logoi are conceived as parts of a
unitary project of investigation. There is also no doubt that Aristotle has a
certain understanding of the relations between these parts. This under-
standing is strongly dependent upon a speci¬c conception of the natural
world and the substantial assumption that this particular department of
reality is, at least to some extent, intelligible to us. More directly, Aristotle
is persuaded that the natural condition for human beings is to know and
understand the truth, and that we can know and understand a lot about
the natural world if only our investigation is conducted in the appropriate
way. But he is also aware that there are features of the natural world that
we cannot adequately explain. I postpone discussion of this interesting
tension.2 For the time being, I would like to focus on the way Aristotle
presents his inquiry into the natural world in the opening lines of the

1 For helpful comments on this point see Lang (1992: 2“13 and 1998: 3“33).
2 Chapter 4, “The limits of Aristotle™s science of nature.”

1
Aristotle and the Science of Nature
2
Meteorology. It is my intention to show that this presentation is not
neutral with respect to a certain conception of the natural world. A better
grasp of this conception will enable us to understand why Aristotle
conceives of the study of the sublunary and the celestial world as forming
a single science: the science of nature or natural science. A full appreci-
ation of this conception will also help us to understand the precise sense
in which Aristotle™s science of nature is a distinctly organized investigation
of the natural world. Aristotle does not think of the science of nature as a
collection of loosely connected, if not disconnected, investigations. On
the contrary, the investigations listed at the beginning of the Meteorology
are distinct but related. Moreover, a close scrutiny of the opening lines of
the Meteorology shows that these investigations are related in a certain way.
I shall argue that the causal relation that holds together the different parts
of the natural world provides us with the conceptual resources to under-
stand the precise sense in which several distinct natural investigations are
uni¬ed and integrated into a single science.


aristotle™s investigation of nature
What follows is a partial translation of the prologue to the Meteorology:3
(1) Earlier we discussed the ¬rst causes of nature, and natural change in general;
(2) also the stars ordered according to their motion, (3) and the bodily elements,
<establishing> their number, nature, and mutual transformation, (4) and
generation and perishing in general. (5) There remains to be considered a part of
this investigation which all predecessors have called meteorology (meteorologia).
¯
<This part is concerned with> that which happens naturally, but with an order
that is less perfect than that of the ¬rst element of bodies, and which takes place
in the region nearest to the motion of the stars. Such are the Milky Way, the
comets, and the movements of meteors. <It studies> also the affections we may
call common to air and water, and the kinds and parts of earth and the affections
of its parts. These throw light on the causes of winds and earthquakes and all the
consequences the motions of these kinds and parts involve. Of these things some


3 This passage not only contains a recommendation regarding the order of investigation of the
natural world but also establishes the relevant relationships among the different natural writings. I
limit myself programmatically to discussing this passage as containing a recommendation
regarding the order of investigation of the natural world. For a recent study of the opening lines
of the Meteorology as evidence for the relationships that hold among the different natural writings,
I refer the reader to Burnyeat (2004: 7“24). Lately Myles Burnyeat has been advocating the view
that Aristotle is a systematic philosopher in the sense that he holds strong views about the
appropriate order of learning and study. The reader who is interested in this topic should read
Burnyeat (2001) and Burnyeat (2002: 28“90).
Aristotle™s science of nature 3
puzzle us while others admit of explanation in some degree. Further, <this
inquiry is concerned with> the falling of thunderbolts, whirlwinds and ¬re-
winds, and further, the recurrent affections produced in these same bodies by
concretion. (6) Once we will have dealt with these things, we will consider
whether we are somehow able to give, in accordance with the method indicated,
an account of animals and plants, both in general and separately. (7) Once this is
discussed, perhaps the whole of what we established at the outset will be
complete (Meteor. 338 a 20 “ 339 a 9).4
Aristotle is about to engage in a new study “ meteorology, meteorologia
¯
“ and ¬nds it important to begin by placing this study within his larger
project of inquiry into nature. Why? The phrase ta meteora was com-
¯
monly used to refer to the totality of the phenomena which take place in
the sky, including the celestial ones.5 This explains why Aristotle cannot
take it for granted that people understand what he means by meteorologia,
¯
but rather has to establish the place that this study occupies in his larger
project of investigation of nature. By so doing, however, he offers some
information about the project in which he is engaged and the way he
conceives of it.6


4 For a vindication of the authenticity of this prologue see Cappelle (1912: 514“35).
5 Anaxagoras was commonly regarded as the champion of this sort of study. In the Phaedrus we are
told that Pericles learnt from him “high speculations about <what is high in> nature” “
meteorologia physeos peri (269 c “ 272 b). More explicitly, Pericles learnt from Anaxagoras
¯ ¯
speculations about what is high in nature; that is speculations about ta meteora. But the
¯
speculations about ta meteora are also high-¬‚own speculations of little use in life. Concern about
¯
ta meteora is a prominent feature in Aristophanes™ portrait of Socrates in the Clouds. See Clouds
¯
225“35. In saluting Socrates, the Clouds say that they would not listen to any other of the
meteorosophistai of the time except Prodicus. See Clouds 358“60. The meteorosophistai are the
¯ ¯
teachers of what is high in nature but also of super¬‚uous accomplishments (both ta meteora and
¯
sophistai have a double meaning in this case). Such hostility to the study of ta meteora was not
¯
uncommon in the ¬fth and fourth centuries bce. This study was regarded as useless and obscure;
the thought was that it did not deliver results because ta meteora are beyond the grasp of human
¯
cognitive capacities. The Hippocratic author of On Ancient Medicine, for example, contrasts his
expertise with “the study of the things in the sky and below earth” (VT i 3.7). In this study, it is
not clear either to the speaker himself or to his audience whether what is said is true or not, since
there is no criterion to which one should refer to obtain clear knowledge (VT i 3.8“10). For an
exhaustive discussion of the usage of the phrase ta meteora in the ¬fth and fourth centuries bce,
¯
see Cappelle (1935: 315“58).
6 In clause (5) Aristotle provides the agenda of meteorology. This consists of a list of phenomena
that meteorology is expected to discuss. This is clearly part of an attempt to revise the received
conception of the discipline. At any rate, Aristotle was not completely successful in his attempt to
revise the view that ta meteora are the totality of the phenomena that take place in the sky. Both
¯
in the Hellenistic and in the post-Hellenistic tradition the phrase ta meteora continued to be used
¯
for all the phenomena that take place in the sky, including the celestial ones. It is signi¬cant, I
think, that Theophrastus felt the need to change the name of Aristotle™s discipline from
meteorology to metarsiology “ from ta metarsia “ precisely in order to avoid the ambiguous
reference to ta meteora. On this terminology and what it implies, see Cappelle (1913: 321“58).
¯
Aristotle and the Science of Nature
4
There is no doubt that Aristotle™s investigation is carefully structured: it
begins with an examination of the ¬rst causes of nature and natural
change in general, continues with a study of the celestial region, and ends
with an investigation of the sublunary world, including a study of plants
and animals. The examination of the ¬rst causes of nature and natural
change in general “ clause (1) “ is a compressed but precise description of
the content of the Physics.7 By dealing with nature and change, the Physics
provides a foundation for the entire investigation of the natural world.8
The language is speci¬cally designed to insist on the generality of the
Physics. By saying that the Physics is concerned with the ¬rst causes of
nature and change in general, Aristotle makes it clear that the Physics
provides the explanatory resources and the principles for a sensible investi-
gation of the natural world. But does the Physics provide all the explana-
tory resources and all the principles for all natural investigations? The
answer is emphatically no. PA 1 is a relatively self-contained and inde-
pendent logos devoted to developing principles that are speci¬c to the
study of animal nature. If the Physics provided all the explanatory re-
sources and all the principles that are necessary for a sensible study
of animal nature, there would be no need of a speci¬c introduction
to the study of animals.9 It is signi¬cant, I think, that the opening
lines of the Meteorology leave it open whether the study of animals and
plants can be exhaustively conducted in accordance with the method
indicated “ clause (6).

7 In late antiquity it was generally agreed that Aristotle™s Physics consisted of two parts. According
to Philoponus and Simplicius, Aristotle and his pupils referred to the ¬rst four logoi of the Physics
as ta peri archon, and to the last three logoi as ta peri kineseos. Simplicius informs us of the
¯ ¯¯
existence of another division: the ¬rst ¬ve logoi were thought to form ta peri archon, and the last
¯
three ta peri kineseos. The prologue to the Meteorology, and in particular the description of its
¯¯
contents as an examination of (i) the ¬rst causes of nature, and (ii) natural change in general, may
have encouraged the division of the Physics into two parts. But there is no reason to think that
this division goes back to Aristotle. On this point see Brunschwig (1991: 11“39) and Barnes (1997:
1“69). See also Pellegrin (2003: 265“71).
8 Myles Burnyeat would say that the Physics provides a “conceptual foundation” for the study of
nature. See Burnyeat (2004: 19“20).
9 On PA 1 as a logos devoted to establishing methodological standards for the study of animal
nature, see Lennox (2001a: 133“43). A discussion of the way in which PA 1 does not only specify
but also builds on the general account of nature offered in the Physics goes beyond the scope of
the present study. I refer the reader to Code (1997: 127“43). This article contains a discussion of
the way in which PA 1 completes the general account of causality offered in the Physics. In Phys. 2
Aristotle is not content to present his general account of causation and discuss how luck and
chance ¬t it. The ¬nal section of Phys. 2 is devoted to explaining why nature (together with
thought) is a ¬nal cause, and what place necessity has in the study of nature. However, the
discussion offered in Phys. 2 is only partial, and Aristotle returns to this topic in PA 1. It is only in
PA 1 that Aristotle argues for the methodological priority of the ¬nal over the moving cause.
Aristotle™s science of nature 5
The study of animals and plants comes at the end of the program of
investigation. Once an account of animals and plants is offered, perhaps
the investigation of nature will be complete “ clause (7). At least two
things are to be noted here. First of all, we only have a study of animals,
and perhaps Aristotle has left only a study of animals. His references to
works on plants are always impersonal and could be referring to the work
of a Peripatetic colleague such as Theophrastus.10 Secondly, and more
importantly, Aristotle presents the study of animals as a part of the science
of nature. This is con¬rmed by what Aristotle says in PA 1, the of¬cial
introduction to the study of animals. There Aristotle presents the study of
animals as “an inquiry into nature” (639 a 12). He describes this study as
“a theoretical <science> concerned with nature” (640 a 2, 641 b 11), and
as “an investigation of nature” (644 b 16). He says that “the inquirer into
nature” is concerned with both the soul and the matter, but more with the
soul (641 a 29“30). Finally, he wonders whether the whole soul, or only a
part of it, is the province of “the <science> of nature” (641 a 33“4). This
language is mildly surprising, especially if one considers that in PA 1
Aristotle concerns himself, by his own admission, solely with animal
nature (645 a 5“6). Why does Aristotle insist on nature if his focus is
animal nature? Aristotle conceives of the study of animals as a speci¬c
investigation. For him, the relevant explanatory principles are to be
biologically speci¬c in order to provide an adequate explanation of animal
life. In the end, the investigation of animal nature requires a reference to a
soul of a speci¬c type as form, and to a living body of a speci¬c type as
matter. At the same time, Aristotle wants to disabuse us of the view that
the study of animal nature is an independent investigation. In other
words, the speci¬city of the study of animal nature does not involve a
denial of the explanatory unity of the science of nature.
Since Aristotle speaks of animals and plants, he obviously regards the
study of animals as a discrete investigation. He is persuaded that we are
able, at least in principle, to draw a line between animals and plants:
animals have a share in cognition; plants do not. Here is how Aristotle
makes this point in GA:
The function of an animal is not only to generate, which is in fact common to all
living beings; in addition, all animals partake in a form of cognition [gnosis], ¯
some more, some less, some very little indeed. For they have perception
[aisthesis], which is a form of cognition . . . it is by perception that animals [zoia]
¯ ¯
differ from merely living beings [zonton monon] (GA 731 a 30“5 and 731 b 4“5).
¯¯

10 I owe this point to Jim Lennox.
Aristotle and the Science of Nature
6
For Aristotle, plants are merely living beings, zonta; but they are not
¯
zoia, because they have no share in perception, which is a form of
¯
cognition. Aristotle is clearly reacting to a certain tendency to connect
the name zoion with the verb for living and being alive, zen. From Plato™s
¯ ¯
Timaeus, for example, we learn that everything that partakes of life,
whatever it might be, can be rightly named zoion, “living being” (Tim.
¯
77 b 1“2). The connection between the name zoion and the verb zen
¯ ¯
explains why in the Timaeus plants are introduced as a second class of zoia ¯
alongside men (Tim. 77 a). Plants are recognized as zoia because they are
¯
living beings (Tim. 77 a). I shall return to the ambiguity of the name zoia ¯
in due course. For the time being, suf¬ce it to say that the term zoia can
¯
be used to refer to all the living beings that there might be, including
plants.11 The fact that Aristotle normally uses the term zoia to refer to
¯
animals, to the exclusion of plants, is ultimately due to his conviction that
animals are a distinct class of living beings, and animal life is a form of life
different from plant life. Later on I shall argue that the DA provides the
explanatory resources and the conceptual framework for an optimal study
of animal life. For the time being, I am content to say that the ¬rst yet
crucial step for an optimal study of animal life is an argument for the view
that animals are a distinct class of living beings. It is precisely by relying
on the results achieved in the DA that Aristotle can restrict himself to a
study of animals and set aside a study of plants.12
But how does Aristotle conceive of the study of animals? Jim Lennox
has recently drawn attention to the cross-references within HA, PA, GA,
and IA. He has shown, to my mind successfully, that these works are all
parts of a single, uni¬ed investigation. He has also shown that this single,
uni¬ed investigation displays a de¬nite structure of a certain type. Put
differently, Aristotle credits the study of animals with unity, structure,
speci¬city, and discreteness, but he does not recognize this study as an
independent investigation.13

11 But it would be a mistake to think that the term zoia is ambiguous only between (1) all living
¯
beings, including plants, and (2) animals, to the exclusion of plants. In the Timaeus the name zoion
¯
is attributed to any living being that there might be, including any living being superior to man
that there might be. Stars are recognized as zoia, on the crucial assumption that they are alive
¯
(Tim. 39 a; 39 e); moreover, the sensible world as a whole is a zoion (Tim. 30 b). I owe this
¯
clari¬cation to Michael Frede.
12 Cf., for example, PN 467 b 4, 468 a 31, 442 b 25, and GA 716 a 1, 783 b 20.
13 J. G. Lennox, “The Place of Zoology in Aristotle™s Natural Philosophy,” presented at the Classical
Philosophy Colloquium, Princeton, December 1“2, 2001. A revised version of this paper was given
as the Keeling Lecture in the fall of 2003 and is now published in Lennox (2005: 55“71). Lennox
rightly says that “this structure has nothing to do with the order in which the actual investigations
were done nor with the order in which works were written” (57). The reader is expected to go
Aristotle™s science of nature 7
PA 1 con¬rms the idiosyncratic way in which Aristotle conceives of the
study of animal nature. In this logos Aristotle insists not only on the unity
of the science of nature but also on its structure, placing the study of
animal nature after the study of the celestial substances:
since we have already dealt with those substances [¼ the celestial substances],
saying what appears to be the case to us, it remains to speak of animal nature,
trying to omit as far as possible nothing, however noble or ignoble it may be (PA
645 a 4“7).
We may or may not believe that this passage is reminiscent of the
beginning of the Meteorology (this is, in fact, open to debate), but there is
no doubt, I think, that the study of animal nature is regarded as part of a
larger inquiry, itself structured in a speci¬c way.

the place of the study of the celestial world in
aristotle™s investigation of nature
From the opening lines of the Meteorology we learn that the study of
animals and plants comes at the end of a large and ambitious program of
investigation. But why does it come at the end of this program? There is
no doubt that certain conceptual resources are presupposed in the study of
animals. For example, since animals and plants are perishable beings, we
have to be clear about the nature of perishing. We have to know, in
particular, that perishing is a case of going out of existence rather than a
case of becoming something else. This helps us to understand why an
investigation of generation and perishing is mentioned at the beginning of
the Meteorology “ clause (4) “ and why this investigation comes before the
study of animals and plants “ clause (6). This investigation is conducted

through these writings in a certain order. A discussion of this order is not immediately relevant to
the present discussion. I am content to claim that the reasons for this order are to be found in PA
1, both in the distinction Aristotle here makes between gathering the data and providing causal
explanations (639 b 8“10), and in his defense of the primacy of the ¬nal (formal) principle over the
moving principle (639 b 15 “ 640 b 5) and the material principle (640 b 5 “ 641 a 17). For example,
the study of the moving principle and the parts that are functional to reproduction (GA) comes
after the study of the other bodily parts (PA). Aristotle provides a reason for this order at the very
beginning of GA: the ¬nal (formal) principle comes ¬rst, and the material and the moving
principle occupy second and third place respectively (715 a 4“6). There is no doubt that the reader
of GA is expected to be already familiar with PA 1 and with the arguments that Aristotle offers
there for the primacy of the ¬nal (formal) principle over the moving principle. On the relationship
between the PA and the GA, see also Code (1997): “we need to know in a detailed way how and
why the ousia is the way it is before we can account for the way in which the ef¬cient cause
operates. Knowledge of the ef¬cient causes by means of which animals are generated is posterior to
knowledge of their ¬nal causes” (143).
Aristotle and the Science of Nature
8
in the GC.14 It is signi¬cant, I think, that some familiarity with this
treatise seems to be presupposed on the part of the reader of the DA
and the biological treatises.15 This does not explain, however, why the
study of the celestial region comes before the study of animals and plants.
The Meteorology is nevertheless crystal clear on this point: the study of the
stars ordered according to their motion occupies second place in the in-
quiry into nature and comes before the study of any aspect of the
sublunary world “ clause (2).16 At ¬rst sight, this is a little surprising.
There are two, if not three, good reasons to expect the study of the
sublunary world to precede, rather than to follow, the study of
the celestial world. To begin with, Aristotle admits that the study of the
celestial world is more dif¬cult, and that our grasp of the celestial bodies is
slight, especially if confronted with what we can know about <plants
and> animals (644 b 32 “ 645 a 7). In addition, Aristotle insists on the
existence of similarities between the celestial and the sublunary world, and
claims that these similarities play a signi¬cant role in the study of the
celestial world. Finally, at one point he even says that the study of <plants
and> animals offers in exchange a certain grasp of the celestial bodies
(645 a 3“4).17 Why, then, should this study come after, rather than before,
the study of the celestial world?
It is not dif¬cult to ¬nd a ¬rst, tentative answer to this question.
Aristotle is not the ¬rst thinker to engage in an investigation of the
natural world in its entirety. At the time there was an already established
tradition of inquiry into nature, which is registered and transmitted by
Plato in the Timaeus. According to this tradition, the student of nature
was expected to put all natural explanations into the context of an overall
narration whose order of topics is ¬rst the heavens, then the elements, and
¬nally the living beings.18 There is no doubt that this is exactly the order

14 On the GC as a study of generation and perishing in general and its foundational character for the
sublunary science of nature, see Burnyeat (2004: 7“24).
15 Aristotle seems to refer to the GC at DA 417 a 1“2, 423 b 29; PA 640 a 9“10, 646 a 15, 645 b 9“11.
16 PA 1 con¬rms that the study of animal nature comes after the study of the celestial bodies
(645 a 4“5).
¨ ¨
17 Here I follow During and his interpretation of the dif¬cult antikatalattetai in 645 a 3. Cf. During
(1943: 120).
18 Strictly speaking, the Timaeus does not provide an investigation of the natural world in all its
aspects. Plato is remarkably shy about animals and plants. However, this is to be understood in
the light of the fact that the Timaeus is programmatically an account of “the all” down to the
generation of “man” (see, for instance, 90 e 1“3). Once an investigation of the human body
(pathology and anatomy included) is offered, the program is completed. In spite of this
programmatic restriction, there is no doubt that the Timaeus consists of a general, uni¬ed account
of the natural (better: sensible) world in terms of which all the natural phenomena can be, at least
in principle, explained.
Aristotle™s science of nature 9
that Aristotle follows in the opening lines of the Meteorology. However, if
we want to understand why Aristotle insists on speaking of inquiry into
nature, and indeed places the study of animals after the study of the
celestial world, we cannot be content with a generic appeal to the pre-
Platonic tradition of inquiry into nature. Aristotle routinely presents
himself as continuing the tradition of the physiologoi. At the beginning
of the Physics, for example, Aristotle puts himself in direct continuity with
this tradition, and makes his own position grow out of the opinions and
results achieved by his predecessors. But his position is not merely the
culmination or perfection of this venerable tradition. It is a dramatically
new position.
I would like to make a fresh start from a well-known Aristotelian
“slogan”: “it takes a man to generate a man.”19 Among other things, this
slogan is designed to point to the fundamental fact that the generation of
a man can be understood only in the light of the nature of the man.
However, a slightly revised version of this slogan can be read in the
Physics: “it takes a man and the sun to generate a man” (194 b 13).
Interestingly enough, the revised slogan occurs also in Lambda. From
Lambda we learn that the explanatory factors involved in the generation
of a man are earth, water, air, and ¬re, a particular form of organization as
the goal of the generation, the father, and ¬nally the motion of the sun
around the ecliptic (1071 a 11“17). In this compressed text, Aristotle is
doing several things at once.20 Among other things, he is trying to
establish the explanatory role that both the father and the sun have in
the generation of a man. Notoriously, Aristotle admits a plurality of
explanatory principles: material, formal, ¬nal, and moving principles.
According to him, both the father and the sun are moving principles,
but they are related to the man in different ways. Father and son are the
same in form; more precisely, the father is in actuality what the earth,
water, air, and ¬re that will become the man are potentially.21 The sun,
unlike the father, is a moving principle of the man without being the same
in form. It is a moving principle “ or better, a remote moving principle “
through its characteristic motion around the ecliptic; by so moving it
indirectly secures the continuous generation of man from man, and hence
the eternal permanence of the species.

19 From Bonitz (1870) we learn that this slogan occurs at Phys. 193 b 8, 198 a 26, 202 a 11; GC 333 b 7;
PA 640 a 25, 646 a 33; GA 735 a 21; Metaph. 1032 a 25, 1033 b 32, 1049 b 25, 1070 a 8, b 34,
1092 a 16.
20 For a close discussion of this text in its context see Code (2000: 161“79).
21 A complication: from Theta 7 we are told that earth, water, air, and ¬re are not potentially the
man (1048 b 37 “ 1049 a 1).
Aristotle and the Science of Nature
10
I have insisted on the slogan that it takes a man and the sun to generate
a man because I am convinced that this slogan sheds some light upon a
substantial assumption that Aristotle makes about the character of the
natural world. First of all, Aristotle is persuaded that the natural world is
an arrangement or organization of a certain kind; that is, a certain kind of
cosmos. Secondly, and more importantly, Aristotle thinks of this cosmos as
a uni¬ed whole “ in Greek holon. The parts of this uni¬ed whole are
causally related to one another in a certain way. The celestial and the
sublunary world are related to one another in such a way that the celestial
world acts on the sublunary world. More speci¬cally, the outer part of the
sublunary world is immediately in contact with the lower part of the
celestial world.22 On Aristotle™s account, what acts on something is
normally affected by it. But this particular case represents an exception
to the rule. The celestial world acts on the sublunary world but it is not
affected by it. Why? For Aristotle, reciprocal action takes place only when
the matter is the same (324 a 34“5).23 The celestial and the sublunary
world are not the same in matter. I postpone discussion of this crucial
aspect of the theory to the following chapters. For the time being, I am
content to say that Aristotle is famously committed to the view that the
celestial world is made of a body which has the capacity to perform
circular motion but does not have the capacity to be affected by anything:
the so-called ¬fth body or ¬fth element.24 By simply performing its
characteristic circular motion, this particular body has an in¬‚uence
on the living and non-living beings populating the sublunary region.


22 Remember that Aristotle does not believe in action at a distance; under the appropriate
circumstances A acts on B if, and only if, A is immediately in contact with B, or A is in contact
with some suitable medium C which, in turn, is in contact with B.
23 Aristotle™s notion of matter cannot be reduced to the notion of material out of which something
is made. From Zeta we learn that matter is that which is capable of being and not being (1032 a
20“1). From Lambda we learn that matter is that which has the capacity for both <contraries>
(1069 b 14“15). Finally, from the GC we learn that matter, qua matter, is capable of being acted
upon (324 b 19). It is by resting on the last passage that Aristotle can claim that:
1. Of the things that can act on something else, those of which the form is not in matter cannot be
acted upon (324 b 5“6).
2. Of the things that can act on something else, those of which the form is in matter can be acted
upon <provided that the matter is the same> (324 b 6).
24 But Aristotle never makes use of the expressions “¬fth element” or “¬fth body.” He also refrains
from using the name aither to refer to the simple celestial body. In the DC, Aristotle is content to
¯
register that aither is the traditional name for the upper part of the world (270 b 20“1). It is
¯
unfortunate that Aristotle™s reticence in using aither is not appreciated enough. The fact that
¯
Aristotle avoids this word is often overlooked, if not obscured and denied, by routinely referring
to Aristotle™s celestial simple body as aither. I shall return to Aristotle™s language in the Epilogue.
¯
Aristotle™s science of nature 11
Aristotle thinks of the living and non-living sublunary things as con¬gur-
ations that come into existence, endure for a while, and ¬nally go out of
existence. He never conceives of these ephemeral con¬gurations in isol-
ation. Both synchronically and diachronically they are conceived as part
of a larger system, which ultimately coincides with the totality of the
sublunary world they contribute to preserve. Diachronically they are parts
of an everlasting process of generation and perishing that has no begin-
ning and no end. Towards the end of the GC, Aristotle makes it clear that
the continuity of this process can be secured only by the continuous
celestial motion (336 a 14“18). At ¬rst, we might ¬nd it dif¬cult to
understand why the everlastingness of the process of coming into exist-
ence and going out of existence requires the existence of an individually
everlasting motion. But we should bear in mind that going out of
existence involves the liberation of a quantity of earth, water, air, and
¬re. These bodies are the material principles of everything in the sublun-
ary world, and for Aristotle they are endowed with the capacity to move
towards their own natural places. Under the appropriate circumstances
they are naturally moving towards these places.25 Something is therefore
needed to prevent the liberated material principles from being completely
relocated in their natural places. The dislocation of a certain amount of
earth, water, air, and ¬re is in fact crucial for the persistence of the process
of coming into existence and going out of existence. By keeping a
minimal level of agitation in the sublunary world, the celestial motion
crucially contributes to the maintenance of a quantity of dislocated
earth, water, air, and ¬re; by so doing this motion crucially contrib-
utes to preserving the relevant level of mixture in the sublunary world
(337 a 1“7).26
By now it should be clear that the program for the investigation of
nature presented in the opening lines of the Meteorology, is strongly
dependent upon a speci¬c conception of the natural world. Aristotle
seems to think of the natural world as a causal system of a speci¬c type.
I add the quali¬cation “of a speci¬c type” because the direction of the
explanation within this causal system is from the celestial to the sublunary
world only. This particular feature of the causal system helps us to
understand why some grasp of the celestial world is for Aristotle not only
necessary but also preliminary to the attainment of an understanding of
important features of the sublunary. However, a few words of clari¬cation

25 More on this point in chapter 2, “Bodies,” and chapter 3, “Motions.”
´
26 On this aspect of Aristotle™s theory, see Bodnar (1997b: 81“117).
Aristotle and the Science of Nature
12
regarding the limits of my last remark are needed. To begin with, there
are features of the sublunary world that can be adequately understood
without taking into account the celestial world. Let us return to the
generation of man from man. There is a sense in which the explanation
of the generation of a particular man from a man can be given by pointing
out four explanatory factors: the father, the sperma, the katamenia, and
the goal of that particular generation; that is, a particular form of
organization realized in a body of a speci¬c type. The sun is required
only to account for the continuity and eternity of the generation of a man
from a man. Moreover, there are only some aspects of the celestial world
which are of direct relevance to the study of the sublunary world. In the
case of the generation of a man from a man, all we need to know is that
the sun performs a speci¬c circular motion; that is, a circulation with a
speci¬c orientation, a certain inclination on the ecliptic, a certain speed,
and so on and so forth. Apparently, we are not required to know why the
sun is engaged in such a motion, and why this motion takes place in the
particular way it does.27 Finally, so far I have focused only on the sun and
insisted that the study of the sun comes before, rather than after, the study
of any aspect of the sublunary world. However, it is fairly clear that the
study of the celestial world in its entirety comes before, rather than after,
the study of the sublunary world. In the opening lines of the Meteorology,
Aristotle speaks of the stars ordered according to their motion “ clause (2).
Aristotle thinks that the job of the student of nature is to provide an
explanation of the behavior of all celestial bodies. He makes it very clear
that the celestial bodies are to be viewed as forming a single integrated
system of a certain type. In the DC, for example, Aristotle engages in a
discussion of two dif¬culties that presuppose the astronomical system of
Eudoxus, and that make sense only if the aim is to provide an explanation
of the behavior of a celestial body as part of a system of interconnected
motions. These dif¬culties are the following: (i) why are the sun and
the moon moved by fewer motions than some of the other planets? (291 b
29“31); and (ii) why are so many stars carried by one single motion “ the
motion of the heaven of the ¬xed stars “ whereas many motions are


27 For Aristotle, any attempt to provide an adequate explanation of the motion of the sun should
start from the assumption that the sun is a living being endowed with the capacity for cognition
and desire. I postpone discussion of the idea that celestial motion is a special type of animal
motion. See chapter 3, “Motions.” For the time being, I limit myself to saying that for Aristotle
celestial bodies keep everything in constant motion by being continuously moved, on the crucial
assumption that they are equipped with some form or other of celestial cognition and celestial
desire.
Aristotle™s science of nature 13
needed to carry one, single planet? (292 a 10“14).28 The requirement that
all the motions of all the celestial bodes are to be considered together is at
work also in Lambda. In chapter 8 of Lambda, Aristotle uses astronomy to
determine the number of the divine intellects that are needed to account
for celestial motion. In this context, Aristotle assumes that the motions of
the heavens form a single interacting system and are to be treated as such
by astronomers.29
As Burnyeat himself says, “it is tempting to take this thought a stage
further” and wonder whether Aristotle conceives of the natural world as a
teleological system. In other words, it is tempting to wonder whether
Aristotle conceives of the natural world as a causal system that exists for
the sake of a de¬nite goal. But it is dif¬cult to see what this goal could be.
Burnyeat is content to gesture at the living creatures that inhabit the
sublunary world as a possible goal for the entire causal system. On this
interpretation, everything, including the celestial bodies, would exist for
the sake of the formation, preservation, and reproduction of the living
organisms that we encounter on earth.30 I count myself among “the sober
readers” of Aristotle. I ¬nd the temptation to think of the natural world as
a teleological system that exists for the sake of the sublunary creatures
resistible, even if the thought is that the entire causal system exists for the
bene¬t of the living creatures that inhabit the sublunary world.31
28 I shall return to these dif¬culties in the discussion of voluntary motion in chapter 3, “Motions.”
29 On the one-system requirement and its astronomical and philosophical signi¬cance, I refer the
reader to Beere (2003: 1“20).
30 Burnyeat (2004: 23“4).
31 Aristotle can use the expression “for the sake of which” to refer not only to the goal but also to the
bene¬ciary. In the Politics, for example, we are told that plants are for the sake of beasts, and beasts
for the sake of man (1256 b 15“22). Here the view seems to be that plants and beasts are subservient
to the end of procuring food and clothing for man. In other words, plants and animals have
internal goals, but they exist and function also for the bene¬t of man. For a passionate attempt to
articulate a speci¬c version of the thought that the natural world, or perhaps its sublunary region,
exists for the sake of human beings, see Sedley (1991: 179“97). According to Sedley, “[for Aristotle]
the entire content of the natural world, including not only plants and animals but perhaps even
seasons and weather, exist and function primarily for the bene¬t of man” (180). Matthen (2001:
171“99) has argued that the natural world of Aristotle is “a single teleologically structured entity”
(182). But the teleology Matthen ascribes to Aristotle is signi¬cantly different from the one
suggested by Sedley. On Matthen™s reading, the natural world does not exist and function for the
sake of a bene¬ciary, but it exists and functions for the sake of “an internal goal” (183). On this
interpretation, the natural world is “so organized as to achieve an end proprietary to its own
essence” (181). The present book is an indirect argument against an interpretation of Aristotle™s
cosmology of this type. I shall argue that the natural world, as it is understood by Aristotle, admits
an important discontinuity between the celestial and the sublunary regions. If I am right, the
discontinuity in question is compatible with the view that the natural world is a single thing, but
not with the view that the natural world has an essence. More directly, I shall argue that the
natural world is a certain arrangement or organization of celestial and sublunary bodies and as
such displays a structure of a certain type, but the structure in question is not a form. De caelo i 9,
Aristotle and the Science of Nature
14
causal unity
Interesting consequences as well as special problems follow from this
particular approach. In particular, we are expected to be able to explain
not only why the inquiry into nature displays a speci¬c structure, but also
why there is only a single inquiry. In other words, we are expected to be able
to identify what gives unity to this inquiry; what makes it one inquiry
rather than a mere collection of relatively independent and suf¬ciently self-
contained investigations. This question can be approached in another way.
Aristotle is committed to the view that there are sciences rather than
science. Moreover, he endorses the view that each science is concerned
with a speci¬c genos. The genos is what a science is about “ in Greek to peri
ho.32 The science of nature is no exception to this rule. From the Metaphys-
ics we learn that all sciences are concerned with some genos (1025 b 7“8), and
that the science of nature too happens to be concerned with some genos:
the science of nature too happens to be about some genos of being, namely
about that substance which has the principle of change and rest in itself (Metaph.
1025 b 18“21).33
But if we want to understand why celestial bodies, meteorological
phenomena, animals, and plants are not an arbitrary division of reality
but a genos, something more speci¬c about this particular genos is to be
said. More directly, an appropriate conception of this genos is required.
The natural world does not display the unity that is distinctive of the
highest genos (the so-called summum genus) in a speci¬c divisional struc-
ture.34 Simply put, celestial bodies, meteorological phenomena, animals,

as I read it, contains a reference to a structure of a certain type, not to a form. More generally, and
more boldly, the natural world as it is understood by Aristotle is not an hylomorphic compound
and is not subject to hylomorphic analysis.
32 On the genos as the subject-matter of a speci¬c science, see McKirahan (1992: 1“3).
33 I take it that Epsilon 1 is an attempt to expand on the thoughts offered in Gamma 1“3. For the
claim that nature is a single genos see, in particular, 1005 a 34.
34 For a discussion of the unity and structure that the highest genos in a speci¬c divisional tree
minimally displays, see Falcon (1996: 127“46). Aristotle has several ways of reminding us that the
highest genos in a divisional tree displays unity together with a minimal amount of structure. At
the beginning of the Categories, for example, footed, winged, aquatic, and two-footed are offered
as differences in animals (Cat. 1 b 8“19). The example is notoriously dif¬cult and elliptical. On the
one hand, footed, winged, and aquatic are coordinate differences. In the Aristotelian jargon
coordination is a relationship between differences that are simultaneous, mutually exclusive, and
provide an exhaustive division of the genos. With the addition of two-footed, however, co-
ordination is destroyed. This addition is to be understood, I think, as a reminder that a genos “ in
this case animal “ is an ordered structure characteristically involving priority, posteriority, and
simultaneity. Put differently, the addition of two-footedness to the list of differences provides the
genos animal with the minimal amount of structure required.
Aristotle™s science of nature 15
and plants form one department of reality, but they do not fall under
some higher genos like the different species of animals do. We have
therefore to look for the relevant generic unity. One possibility is to argue
that the science of nature is a methodologically uni¬ed science and claim
that methodological unity is enough to secure the required generic unity.
Let us return to the beginning of the Meteorology, and in particular to the
question whether the study of plants and animals can be exhaustively
conducted in accordance with the method indicated “ clause (6). I have
argued that the study of animals and plants requires additional principles
speci¬c to the particular objects of study. At the same time, there is no
doubt that the study of plants and animals is conceptually related to the
other natural investigations and is conducted in accordance with the
principles indicated in the Physics. In the Physics, Aristotle makes it clear
that the science of nature is the result of a search for the relevant explana-
tory principles: the principles of change. Aristotle is committed to the
view that change is the distinctive feature of the natural world and
famously argues for the existence of four principles of change: matter,
form, the moving principle, and the goal. In the Physics, Aristotle claims
that the job of the student of nature is to search for “all of them” (198 a
22“3). In this passage, Aristotle has in mind primarily the study of the
sublunary world. But there is evidence that he does not intend to con¬ne
his claim to the study of this region of the natural world. He conceives the
entire science of nature as the result of a search for these four explanatory
principles. This point is explicitly made towards the end of the GC. Here
Aristotle claims that the relevant explanatory principles are the same in
number in the study of both the celestial and the sublunary world (335 a
28“9). Note, however, that Aristotle does not say that the student of
nature is looking for the same explanatory principles, but for the same
type of explanatory principles. The study of celestial bodies, meteoro-
logical phenomena, animals, and plants forms one and the same science
because the search for a speci¬c explanation is conducted on the assump-
tion that four types of explanatory principles are relevant for an adequate
explanation: matter, form, the moving principle, and the goal.
Aristotle defends the thesis that there is explanatory unity in the natural
world; that is, that there are four types of principles in the natural world;
at the same time, he insists on the speci¬city and appropriateness of these
principles. Consider the case of matter. From the Metaphysics we learn
that the student of nature is concerned with natural substances: the
substances that have a nature as an internal principle of motion and rest
(1025 b 18“21). For Aristotle, these substances are essentially realized in
Aristotle and the Science of Nature
16
some matter or other. To put it in another way, the natural substances are
essentially material substances. The job of the student of nature is to study
these substances without omitting their material aspect or reducing them
to their material aspect only. Yet these substances need not be realized in
the same matter. Aristotle is ¬rmly persuaded that there is no material
unity in the natural world. He is able to speak of matter without
committing himself to the thesis that there is one and the same material
out of which everything in the natural world is made. I shall return to this
crucial aspect of the Aristotelian doctrine of matter in due course.35 For
the time being, I am content to say that Aristotle believes in the existence
of celestial matter as a signi¬cantly different type of matter from the one
we encounter in the sublunary world.
At any rate, the unity of genos is not just the unity of method. The
different parts of the program outlined at the beginning of the Meteorology
are held together by explanatory unity. But this explanatory unity ultim-
ately rests upon causal unity. The different parts of the natural world
are related to one another in such a way that some of them have a
determinate in¬‚uence on the others. By simply performing circular
motion, the celestial bodies secure the continuity of the generation of
one thing from another in the sublunary world. For Aristotle, there would
be no sublunary world without the action of the celestial world. Put
differently, celestial bodies, meteorological phenomena, animals, and
plants have suf¬cient unity to be one genos rather than an arbitrary
division of reality because they are causally interconnected in a speci¬c
way, and the job of the student of nature is to uncover this speci¬c causal
interconnectedness.

is the study of the soul part of the
science of nature ?
In the opening lines of the Meteorology Aristotle makes it very clear that
the study of life belongs to the science of nature. The study of plants and
animals seems to be understood as a central part, if not the culmination,
of the science of nature. But does the study of the principle of life, the
soul, belong to the science of nature? Interestingly enough, Aristotle
makes no reference to a distinct investigation of the soul in the prologue
to the Meteorology. He does say that once the meteorological phenomena
have been addressed we should move to plants and animals and study

35 Chapter 4, “The limits of Aristotle™s science of nature.”
Aristotle™s science of nature 17
them according to the method indicated; however, he does not refer to a
distinct investigation of the soul, either in clause (6) or (7). How is his
silence to be understood? Tentatively, one might try to explain the
absence of a reference to the DA from the beginning of the Meteorology
by appealing to the programmatic nature of this passage. The DA would
not be mentioned precisely because Aristotle is content to outline a
program. Neither a work on the parts nor a work on the generation of
animals is listed at the beginning of the Meteorology. Yet such works
are not excluded from the science of nature as it is presented in this
passage. Why should the case of the DA be different from that of PA
or GA? Indeed the case of the DA is a different one, and I shall try to
explain why.36
There is no doubt that the study of the soul is both relevant and
preliminary to a study of life. Aristotle insists on this point in the opening
lines of the DA. Note, however, that Aristotle does not say that the study
of the soul is part of the study of nature. His language seems to be
carefully designed not to say that the study of the soul is part of the
science of nature:
it also seems that knowledge of the soul contributes greatly to all the truth, but
most especially to truth about nature; for the soul is a sort of principle of zoia
¯
(402 a 4“7).
In this particular case I have decided against translating the word zoia,
¯
37
which is tentative and ambiguous in various ways. In its most general
meaning, zoia refers to all the living beings that there might be, including
¯
any living being superior to human beings that there might be.38 In
the DA zoia is normally used to refer to animals. Aristotle is able to say
¯
that all living beings, zonta, have life, but only animals, zoia, have
¯ ¯

36 The view that the study of the soul is a branch of the science of nature is defended in Wedin
(1988: 3“9). Cf. also Burnyeat (2001: 134n15): “psychology for Aristotle is part of physics: see DA
1.1 with the caveats of PA 1.1.641 a 32“b 10, Metaph. Epsilon 1.1026 a 5“6.” Burnyeat (2002: 28“90,
in particular 36): “his psychology is designed to be the crowning achievement of his physics.” In
the light of this conviction, it is not surprising to discover that Burnyeat can see a reference to the
DA in the opening lines of the Meteorology: “this is a large scale map of Aristotle™s natural
philosophy, beginning with the Physics, going on to the DC and the GC, pausing here for the
Meteorologica, looking forward to the DA and the biological works.” Cf. Burnyeat (2004: 13). The
debate on whether the study of the soul belongs to the science of nature goes back to antiquity.
See [Simplicius], In DA, 1. 23“3. 28. This debate continued in the exegetical tradition in the
format of a preliminary quaestio to the study of the soul. For a convenient, late scholastic
summary of this debate, see the Coimbran authors, In DA, quaestio unica, num intellectivae
animae contemplatio ad physiologicae doctrinam pertineat, an non.
37 I owe this point to Michael Frede.
38 See the passages from the Timaeus that I have quoted in footnote 11.
Aristotle and the Science of Nature
18
perception (413 b 1“4). But this cannot be the meaning that zoia has at the
¯
beginning of the treatise. Aristotle cannot say, at the outset of his investi-
gation, that the study of the soul is relevant, and indeed preliminary, to a
study of animals, let alone animal life (pace Hicks and Hamlyn). He has
¬rst to establish that animals are a distinct class of living beings, and that
animal life is a form of life distinct from both human and plant life. To
assume, right from the beginning, that animals are a distinct class of living
beings, let alone a speci¬c form of life, would amount to denying that the
study of the soul is foundational with respect to the study of animal life
which is conducted in the biological works. In a recent publication,
Geoffrey Lloyd has drawn attention to the role of the DA in the context
of Aristotle™s zoology. He has considered the opening lines of the DA as
evidence for the “zoological orientation” of the treatise and has read it in
the light of the criticism that a few lines below Aristotle raises against his
predecessors, who in considering the soul wrote as if human souls were
the only type of soul (402 b 3“5).39 The zoological orientation of the DA
cannot be disputed. But the ¬rst, crucial step in this project is to show that
the focus on animal life is not the result of an arbitrary decision, but it
rather re¬‚ects the way the natural world is divided. In other words, the
DA provides Aristotle not only with the conceptual resources but also
with a theoretical justi¬cation for his decision to focus on animal life, to
the exclusion of plant life.
Before embarking on the study of the soul Aristotle tells us that this
study will result in knowledge of the soul, and that this knowledge will
contribute to the study of nature because it is relevant to the study of all
living beings, zoia. His view seems to be that in order to study life
¯
optimally, one has to engage in the study of the principle of life, the soul.
However, this does not help us to understand why an investigation of the
soul is not mentioned at the beginning of the Meteorology. On the
contrary, Aristotle™s silence invites a close scrutiny of the considerations
that may have led him to exclude the study of the principle of life, the
soul, from the program outlined at the beginning of the Meteorology. Here
I would like to make two distinct but related points. Together they will
help us to understand, or perhaps to begin to understand, why there is no
reference to the DA in the opening lines of the Meteorology. To begin with,
there is scant yet clear evidence that in the DA Aristotle does not concern
himself with the soul without quali¬cation. A couple of times Aristotle


39 Lloyd (1998b: 38“66).
Aristotle™s science of nature 19
explicitly con¬nes his investigation to the soul of perishable living beings
(413 a 31“2; 415 a 8“9). In the following chapters I shall argue that Aristotle
is a modest investigator and explain why he does not engage in an
investigation of the celestial souls, though he admits that the celestial
bodies are equipped with cognition and desire. For the time being, I am
content to notice that Aristotle™s study of the soul is programmatically
con¬ned to the souls of perishable living beings.40 Secondly, and more
importantly, even this modest investigation, the investigation of the soul
of perishable (¼ sublunary) living beings, goes beyond the boundaries of
the science of nature. In PA 1 Aristotle wonders whether the entire soul, or
only a part of it, is the province of the <inquiry into> nature (641 a 33“
4). He concludes that the inquirer into nature is not concerned with the
entire soul but only with a part of it:
It is clear, then, that one should not speak of the soul in its entirety: for it is not
the soul in its entirety that is a nature, but <only> some part of it (one part or
more parts) (641 b 9“10).
How is this conclusion to be understood? In PA 1 Aristotle argues for
the view that the science of nature does not study the soul in its entirety.41
His argument crucially depends on the following piece of hypothetical
reasoning:
1. If the science of nature studies the soul in its entirety, then it studies
thought [nous].
2. But thought [nous] is of all the objects of thought [ta noeta]. Therefore
¯
3. no philosophy [philosophia] is left besides the science of nature.
The problem with the conclusion (3) is that it con¬‚icts with Aristotle™s
view that the science of nature does not exhaust the totality of what can be
thought. For Aristotle, there are objects of thought that are not studied by
the science of nature. For instance, mathematical objects are objects of


40 In the Aristotelian tradition the study of the soul is programmatically con¬ned to the souls of
perishable living beings. Here is how Alexander of Aphrodisias introduces his own De anima: “It
is our intention to discuss the soul, that of the body liable to generation and perishing. We shall
inquiry into its ousia and its capacities, what and how many these are, and how they differ among
themselves” (DA 1. 1“3). The fact that the study of the soul is programmatically con¬ned to the
soul of perishable living beings should not be taken as evidence for the view that life manifests
itself only in this way. Like Aristotle, Alexander believes that the celestial bodies are alive and
engaged in the eternal and blissful life that is appropriate to their divine status. I shall return to
the topic of celestial life in chapter 3, “Motions.”
41 For a recent discussion of this argument, see Broadie (1996: 163“76, in particular 168“9); Caston
(1996: 177“92, in particular 181“4). See also Lennox (1999: 1“17).
Aristotle and the Science of Nature
20
thought, and they do not fall under the science of nature. The mathem-
atician rather than the student of nature concerns himself with these
objects and their per se properties. This point can be extended to any
body of knowledge that constitutes an Aristotelian science or expertise.
Each Aristotelian science or expertise consists in a system of noeta. If¯
accepted, the conclusion (3) would commit Aristotle to the claim that the
science of nature studies the totality of that which can be grasped by
thought; that is, the totality of that which is intelligible. For Aristotle,
there is therefore a problem with either (1) or (2). But (2) is a piece of
doctrine that Aristotle endorses. For Aristotle, each capacity, including
the capacity for thought, has its correlative objects, and the study of each
capacity results in a study of all the correlative objects. There remains (1)
and the claim that the science of nature studies the soul in its entirety,
including thought. This is the claim that Aristotle rejects. The science of
nature does not study the soul in its entirety. For Aristotle, thought is a
capacity that fully developed human beings naturally possess; at the same
time, however, Aristotle regards thought as a natural capacity that enables
them to progress beyond nature and the natural world.
The boundaries of the science of nature are clearly demarcated in PA 1:
the job of the student of nature is to investigate the soul in so far as it is a
principle of motion and rest “ in so far as it animates a body of a speci¬c
type. His job is to study the soul in so far as this latter is responsible
for the activities that are characteristic of this particular type of living
body. Three types of activities are mentioned: growing, perceiving,42
and moving around. Two speci¬c parts of the soul are also listed: the
part which is present even in plants, and the perceptive part, to aisthetikon
¯
43
(641 b 5“6). There is no doubt that these parts are regarded as the
relevant sources for the activities in question and therefore fall within the
province of the science of nature. A third part of the soul is nevertheless
mentioned in the PA 1: to noetikon. This part does not have a role in the
¯
explanation of the ¬rst two activities mentioned (growing and perceiving).
It can but need not have such a role in the explanation of the moving
around of an appropriate living body; that is, the living body of a human

42 Aristotle speaks of alteration “ in Greek alloiosis. In the DA Aristotle argues that perception is a
¯
sort (tis) of alteration (416 b 34). On how to understand this claim (and the quali¬cation tis) I
refer the reader to Burnyeat (2002: 28“90).
43 Remember that the focus of PA is animal life. By referring to the part which is present even (kai )
in plants, Aristotle explicitly acknowledges that plants are alive. In the DA Aristotle has
established that plants are alive and enjoy a speci¬c type of life, distinct from animal life.
Aristotle™s science of nature 21
being. Aristotle makes this point in the DA: we often follow <our own>
phantasiai against knowledge (433 a 10“11). What appears to be the good
accompanied with the appropriate desire suf¬ces for action. But if this is
the case, for human beings as well as for the non-rational animals,
phantasia, accompanied with the appropriate desire, is suf¬cient for
moving from one place to another.
The position defended in PA 1 is brie¬‚y recalled in the Metaphysics. In
his discussion of the partition of theoretical sciences into the science of
nature, mathematics, and theology, Aristotle claims that the job of the
student of nature is to study “some soul” (1026 a 5). He adds that this is to
be identi¬ed with “the soul that cannot be without matter” (1026 a 6). In
the DA Aristotle argues for the immateriality of thought on the basis of
the fact that there is no restriction on the extent of that which can be
thought (429 a 18). I do not need to enter into a discussion of this
notoriously dif¬cult aspect of Aristotle™s psychology. I only note that
the study of thought (nous) is a crucial part of psychology, and that for
this reason psychology seems to enjoy a special status in the Aristotelian
system. Let us return, ¬nally, to the partition of the theoretical sciences
into the science of nature, mathematics and theology. There is no doubt
that this classi¬cation is meant to be exhaustive and that psychology is to
fall under one of these three broad theoretical sciences if it is a science.
However, the conditional is more than appropriate in this case: given that
the study of the soul does fall under these three broad theoretical sciences
but does not fall completely under any of them, one may wonder whether
for Aristotle the study of the soul is a science at all.44
Perhaps I am now able to say why there is no reference to an investi-
gation of the soul at the beginning of the Meteorology and, more generally,
why Aristotle, in the DA or elsewhere, refrains from saying that the study
of the soul is part of the science of nature. Since Alexander of Aphrodisias

44 Alan Code (in a private communication) tells me that there is a theoretical study of the soul
corresponding to each of the theoretical sciences. This is required by the argument that Aristotle
offers in PA 1 and the idea that thought and its objects are correlatives. But I have already insisted
that a(n Aristotelian) science is always about a speci¬c domain and that this domain has to satisfy
certain constraints. Minimally, it must possess a speci¬c kind of unity “ generic unity. It is just
unclear whether this kind of unity is possible in the account of the soul. An objection: for
Aristotle, the soul is suf¬ciently united to be the object of a single study (pragmateia). My answer
is that the DA is devoted to the soul of the perishable living beings, not to the soul without
quali¬cation. In due course I shall return to this topic. I shall argue that Aristotle has a plan for
the study of the soul. I shall show that this plan crucially depends on a ¬rm grasp of the
boundaries of the investigation of the soul. See chapter 4, “The limits of Aristotle™s science of
nature.”
Aristotle and the Science of Nature
22
it has been routinely suggested that the Meteorology must contain an
implicit reference to the DA and that this implicit reference is to be read
in clause (6).45 On the contrary, there is no reference, either implicit or
explicit, to the DA at the beginning of the Meteorology because the
investigation of the soul, or rather the section of the DA concerned with
thinking and thought, goes beyond the boundaries of the science of
nature. As Aristotle himself puts it at the beginning of the DA, the study
of the soul is relevant for getting to all truth (as opposed to truth about
nature and the natural word only, 402 a 4“7).46




45 Here is how Alexander elaborates on the reference to “the account of animals and plants” in
clause (6):
one will include in the study of animals <the works> (1) on the soul, (2) on perception and the
objects of perception, (3) on memory and sleep and divination through sleep, (4) on youth and
old age, (5) on length and brevity of life, and (6) whatever else has been written by Aristotle and
refers to animals (In Meteora 3.29 “ 4.1).
Note that the investigation of the soul (the DA) is mentioned at the beginning of this passage, and
the short treatises to which we usually refer with the collective title Parva naturalia (PN ) occupy
second place. They are considered a sequel to the DA. For the epistemological status of the PN see
next footnote.
46 On the interpretation I am recommending, Aristotle™s science of nature and his study of the soul
overlap in various ways, but they are distinct disciplines. Aristotle seems to have a ¬rm grasp of
their boundaries. Consider how the short investigations collected under the title PN are
introduced:
(1) Since we have already dealt with the soul by itself and with each of its capacities, (2) we have
next to consider animals [zoia] and all the beings that have life, <investigating> what are their
¯
common and what are their proper activities [praxeis]. (3) Now let it be assumed what has been

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