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THE WORLD PHILOSOPHY MADE
iii
THE
WORLD
P H I LO S O P H Y
MADE
From Plato to the Digital Age
S COT T
S OA M E S
PRINCETON UNIVERSIT Y PRESS
Princeton & Oxford
Copyright © 2019 by Prince ton University Press
Published by Prince ton University Press
41 William Street, Princeton, New Jersey 08540
6 Oxford Street, Woodstock, Oxfordshire OX20 1TR
press.princeton.edu
All Rights Reserved
Library of Congress Cataloging-in-Publication Data
Names: Soames, Scott, author.
Title: The world philosophy made :
from Plato to the digital age / Scott Soames.
Description: Princeton, NJ : Princeton University Press, 2019. |
Includes bibliographical references and index.
Identifiers: LCCN 2019019545 | ISBN 9780691176925 (hardcover)
Subjects: LCSH: Philosophy and civilization. | Philosophy—History.
Classification: LCC B59 .S63 2019 | DDC 306.01—dc23
LC record available at https://lccn.loc.gov/2019019545
British Library Cataloging-in-Publication Data is available
Editorial: Rob Tempio & Matt Rohal
Production Editorial: Ali Parrington
Text and Jacket/Cover Design: Chris Ferrante
Production: Merli Guerra
Publicity: James Schneider, Katie Lewis & Alyssa Sanford
This book has been composed in Baskerville 10 Pro and Futura PT
Printed on acid-free paper. ∞
Printed in the United States of Amer i ca
1 3 5 7 9 10 8 6 4 2
This book is dedicated to my dear wife Martha
without whom it could not have been written
and
to my friend Frank Price
the wisest man I know
CONTENTS
Introduction
ix
Timeline
xiv
1
The Dawn of Western Philosophy
1
2
A Truce between Faith and Reason
20
3
The Beginnings of Modern Science
40
4 Free Societies, Free Markets, and
Free People
73
Modern Logic and the Foundations
of Mathematics
92
Logic, Computation, and the Birth
of the Digital Age
113
7
The Science of Language
133
8
The Science of Rational Choice
157
9
Mind, Body, and Cognitive Science
188
10
Philosophy and Physics
220
5
6
viii
C ontents
11
Liberty, Justice, and the Good Society
250
12
Laws, Constitutions, and the State
303
13
The Objectivity of Morality
341
14
Virtue, Happiness, and Meaning in the
Face of Death
373
Appendix: The Noble Deaths of Socrates
and David Hume
386
Bios of Leading Figures
397
Acknowledgments
405
Notes
407
References
425
Index
435
INTRODUCTION
In May of 2016 I published an article, “Philosophy’s True
Home,” at the New York Times Opinionator blog. The article
was written in response to an e arlier piece, “When Philosophy Lost Its Way” by Robert Frodeman and Adam Briggle,
which contended that western philosophy’s institutionalization in the university in the late nineteenth century
separated it from the study of humanity and nature, and
diverted it from its central task of guiding us to live virtuous and meaningful lives. I responded that recent and
contemporary philosophy in the west had not lost its way,
but, on the contrary, was continuing its record of impressive success both in laying the conceptual foundations for
advances in theoretical knowledge and in advancing the
systematic study of ethics, political philosophy, and h
uman
well-b eing. After the article appeared, my editor, Rob
Tempio, at Princeton University Press, suggested that I explore the topic in a book-length work, which I was initially
not inclined to do.
Before long, however, I became intrigued by the idea and
convinced that it might serve a larger purpose. Having
spent my adult life trying to advance the areas in philosophy at which I am most adept, I had not given sufficient
thought to the overall shape of the discipline and its place
in the modern world. I knew that, in the aggregate, we
philosophers have many productive, though rather specialized, professional contacts with mathematicians,
physicists, biologists, psychologists, linguists, cognitive
x
I ntroduction
scientists, neuroscientists, economists, political scientists,
law professors, historians, classicists, and others. As chairman of the Department of Philosophy at the University of
Southern California, I was also aware of positive receptions our philosophy-led interdisciplinary undergraduate
majors Philosophy, Politics, and Law and Philosophy and Physics have received, which I hope our new offering, Philosophy, Politics, and Economics, will too. But I had, I am afraid,
tended to dismiss, as unalterable, the depth of ignorance
about who we are and what we do among the general educated public, large swaths of academia, and, most importantly, among many of the young who might otherwise
profit from what we have to offer.
Thinking more about it, however, I have become more
optimistic. I now believe that the ignorance I previously
deplored is due, in part, to our own failure as philosophers
to seriously address a larger audience. This book is an attempt to correct that by explaining what western philosophy is, what it has been, and what, I am convinced, it
will continue to be. Contrary to the opinion of many, the
study of western philosophy today is not the study of a
frozen historical canon from Socrates and Plato to Kant,
Hegel, and Nietzsche, offering a smorgasbord of previous
responses to unanswerable questions yielding no genuine
knowledge. Although history remains an important part of
the subject, today’s philosophers generate new philosophical questions, while offering better answers to traditional
questions than those given by earlier thinkers. As a result,
philosophical knowledge is increasing and the canon in philosophy is always expanding.
Philosophers have been, and continue to be, deeply
involved in all important areas of intellectual concern, including the arts, the sciences, and the humanities. Properly
understood, philosophy is not an isolated discipline, but
the partner of virtually all disciplines. Nor is western phi-
I ntroduction xi
losophy the w
hole story. Although this book is concerned
with it alone, many of the remarkable advances in civilization that western philosophy has helped to bring about
have become the common property of all cultures. As more
works in different philosophical traditions are translated
and new bodies of secondary literature grow up, new syntheses will become possible, sparking new philosophical
departures.
In sum, this book is about the contributions philoso
phers have made, and continue to make, to our civilization.
Of course, it w
asn’t philosophers alone, whether western or
not, who made the civilized world we enjoy today. But the
effects of their efforts have been more profound and far-
reaching than is commonly realized. Our natural science,
mathematics, and technology, our social science, political
institutions, and economic life, our education, culture, religion, and our understanding of ourselves have been s haped
by philosophy. This is no accident; it is due to the essential interconnection of philosophy with all foundational
knowledge.
Philosophy never advances against a background of rank
ignorance. It flourishes when enough is known about some
domain to make g
reat progress conceivable, even though
it remains incompletely realized b
ecause new methods are
needed. Philosophers help by giving us new concepts, reinterpreting old truths, and reconceptualizing questions to
expand their solution spaces. Sometimes philosophers do
this when sciences are born, but they also do it as disciplines mature. As science advances, there is more, not less,
for philosophy to do. Our knowledge of the universe and
ourselves grows like an expanding sphere of light from a
point of illumination. As light travels in all directions away
from the source, the volume of the sphere, representing our
secure knowledge, grows exponentially. But so does the
surface area of the sphere, representing the border where
xii
I ntroduction
knowledge blurs into doubt, bringing back methodological uncertainty. Philosophy monitors the border, ready to
help plot our next move.
The reader w
ill, I hope, gain a sense of what this means
when moving through the book. The first six chapters cover
ancient Greece, the Middle Ages, the Renaissance, and the
sixteenth through eighteenth centuries, followed by the late
nineteenth and early twentieth centuries. Th
ere you w
ill
see remarkable advances by all manner of intermixtures of
philosophical thought with mathematical, scientific, politi
cal, and religious thought—sometimes in single minds and
sometimes in communicating minds. The focus will shift a
bit when chapters 7 through 10 move you deeply into the
twentieth century and beyond, examining the genesis of
modern theories of rational decision and action, the efforts
to advance our understanding of language and mind, and
the struggle to make sense of what modern physics is telling us about the universe. H
ere the focus is less on the origins of easily recognizable tangible benefits we enjoy t oday
(though t here are some), and more on the role of philos
ophers, sometimes leading, sometimes merely supporting
and supplementing, the work of specialists trying to bring
order to natural phenomena that are difficult to conceptualize in both emerging and well-established sciences. The
final chapters, 11–14, attack pressing l egal, political, moral,
and even existential questions. Here no problems are definitively solved. The contributions, if they are such, lie in
articulating productive perspectives for attacking them.
I close with an invitation and a warning. Much in this
book reports on the impact of philosophers and their
work on broader areas of thought and action, as well as
the impact of developments outside of philosophy on
philosophy itself. But not all of the reasoning you w
ill
encounter is about philosophy. Some of it is philosophy
itself—expositions of some leading ideas of the great phi
I ntroduction xiii
losophers, criticism and assessment of t hose ideas, and in
dependent reflection on philosophical themes. In short,
some of what you will encounter is philosophical reasoning and argument pure and s imple. Thus, you are invited
not only to review a picture of what philosophy has done
up to now, but to engage with philosophy in the making,
and, thereby, to do a bit of philosophy yourself by critically
assessing the philosophical reasoning you find here.
Renaissance Science
Kepler, Galileo
Trial of Socrates
First University
Plato’s Academy
Summa Theologica
Free People, Free Thought, Free Markets
Locke: Natural Rights, Limited Democratic State
Hume: Voluntary, Evolving Institutions
Smith: Wealth and Economic Freedom
Cogito Ergo Sum
Analytic Geometry
Refraction of Light
Copernican Revolution
Inventing Modern Logic
Set Theory
Foundations of Mathematics
Leibniz
Critique of Absolute Space
Calculus
Ockham’s Razor
Revival of Aristotelian
Study of Nature
Newton
Laws of Motion
Calculus
Establ
Comp
and Lo
Understanding Modern Physics
Relativity and Quantum Mechanics
c State
Rational Decision Theory
Subjective Probability
Agent Relative Utilities
Can Philosophy Reestablish
Moral Objectivity?
Death and the
Meaning of Life
The Study of Language and
Mind becomes Scientific
Mathematical Computability, the Birth of the Digital Age
Godel, Church, and Turing
Establishing the Scope and Limits of Logic
Completeness, Incompleteness
and Logical Consequence
The Struggle for a Principled
Theory of Law and Jurisprudence
New Approaches in
Political Philosophy
THE WORLD PHILOSOPHY MADE
CHAPTER 1
T H E D AW N O F
W ES T E RN P H I LOSO P H Y
The world-transforming goals of Socrates, Plato, and
Aristotle; rational inquiry as the means to theoretical
knowledge of the world and practical wisdom in
the art of living; the intertwining of Greek science,
mathematics, and philosophy; Plato’s Academy;
the later schools of Stoicism and Epicureanism.
There is no better expression of the spirit animating the
birth of western philosophy than the first sentence of
Book I of Aristotle’s Metaphysics, “All men by nature desire to know.”1 What we desire to know includes not only
particular facts, but also general truths that explain such
facts in terms of features of the world that transcend the
varying deliverances of our senses. It was a founding principle of western philosophy that such knowledge requires
precisely delineated concepts—e.g., number, element, point,
line, angle, shape, circle, sphere, circumference, area, dimension,
space, volume, matter, density, body, velocity, motion, direction,
proportion, causation, change, permanence, quantity, and
quality—deployed according to the laws of logic, and used
to formulate principles of mathematics, and universal
laws of nature. In addition to knowledge of the world,
what we seek also includes knowledge of ourselves, our
common human nature, the good lives we aspire to live,
and the good societies to which we hope to contribute. It
was a further founding principle of western philosophy
2
CHAPTER 1
that knowledge of these normative matters can be objective, and so requires precise concepts of goodness, happiness,
virtue, and justice, deployed with all appropriate rigor. It is
to Socrates, Plato, and Aristotle, more than any others, that
we owe these world-transforming ideas.
Of these, the central figure is Plato—in part because
Aristotle was his student, and in part because what we
know of Socrates is derived largely from the Socratesfigure of Plato’s dialogues. Born in Athens in or about 427
BCE, Plato was raised in a culture in which one’s knowledge of the world, one’s place in it, and the models for
one’s conduct were derived largely from imaginative identification with the gods and heroes of orally performed
epic poetry.2 At the time of his birth, the poetry of Homer
and Hesiod was still the primary vehicle of instruction in
Athens. Such poetry was not only, or even primarily, a form
of entertainment; it was, as Walter Burkert says, the glue
that held Greek society and culture together.
The authority to whom the Greeks appealed was the poetry of Hesiod and, above all, of Homer. The spiritual
unity of the Greeks was founded and upheld by poetry—a
poetry which could still draw on living oral tradition to
produce a felicitous union of freedom and form, spontaneity and discipline. To be a Greek was to be educated,
and the foundation of all education was Homer.3
Eric Havelock, whose pioneering work documented the
transformation of ancient Greek culture from oral and narrative to written and rationally critical, saw epic poetry as
a living encyclopedia for transmitting Greek history and
culture to the young. The individual, he observed,
is required as a civilised being to become acquainted
with the history, the social organization, the technical
DAW N O f W E S T E R N P H I L O S O P H Y
3
competence and the moral imperatives of his group. . . .
This over-all body of experience . . . is incorporated in
a rhythmic narrative . . . which he memorizes . . . something he accepts uncritically, or else it fails to survive in
his living memory. Its acceptance and retention are made
psychologically possible by a mechanism of . . . selfidentification with the situations and the stories related
in the performance. . . . “His is not to reason why.”4
This was the mindset Plato set out to change. Deriving
inspiration from Socrates, he sought to transform his culture into a rationally critical one in which all knowledge—
normative and nonnormative alike—was objectively stateable, logically testable, and intellectually defensible. In
short, he attempted to change the culture from one based
on the oral story (narrative) to one based on the written
statement (objective description).5
The monumental change Plato sought, and largely
achieved, did not begin with him; it was already underway
in pre-Socratic philosophy, science, and mathematics.6 The
pre-Socratic philosophers—Thales (624–547 BCE), Heraclitus (535–475), Parmenides (born circa 510), Democritus
(died circa 465), and others—mediated the transformation
from the narrative culture of the Homeric age to the rationally critical culture brought to fruition by Socrates,
Plato, and Aristotle. To take one telling example, prior
to the transition, the Greeks had no word for matter and
no abstract notion of motion applying equally to animate
and otherwise inert bodies. After the transition, they had
measurable conceptions of matter, motion, velocity, shape,
direction, and other abstract concepts that were used to
formulate and test explanatory hypotheses purporting
to be universal laws.7
The pre-Socratic philosophers, who set the stage for
the transition from an oral, narrative culture to a written,
4
CHAPTER 1
rationally critical one, had a foot in both. Unlike the narrators of epic poetry, they were more teachers than entertainers.
Still, they often performed their written compositions, and
so expected more to be heard than read, which affected
their texts, which weren’t treatises in the style of Aristotle.
Greek mathematicians, who were often philosophers and
sometimes astronomers (investigating the trajectories of
celestial bodies), were also crucial to the cultural transformation culminating in Plato and Aristotle. Their important
pre-Socratic achievements included:
The observations (probably not proofs) of Thales (who
famously held that water is the element out of which
everything is constituted)
a) that a circle is bisected by its diameter,
b) that the angles at the base of a triangle with two
equal sides are equal, and
c) that triangles with an equal side and two equal
angles are themselves equal.8
The proofs by followers of Pythagoras
a) that the sum of the angles of a triangle are equal to
two right angles (prior to 450 BCE),
b) that the square of the hypotenuse of a right triangle
is equal to the sum of the squares of the other sides
(prior to 450),
c) that the square root of 2 is irrational, i.e., a number
that can’t be expressed as a fraction (prior to 450),
and
d) that the square roots of 3, 5, 7, 11, 13, and 17 are (like
that of 2) also irrational (Theodorus, pupil of Protagoras and teacher of Plato, circa 400).9
The discoveries by Democritus (who developed the classical metaphysical theory of atomism)
a) that the volume of a cone is ⅓ that of a cylinder
with the same base and height, and
DAW N O f W E S T E R N P H I L O S O P H Y
5
b) that the volume of a pyramid is ⅓ that of a prism
with the same base and height.10
The proof by Hippocrates (circa 440) that the ratio of
the areas of two circles equals the ratios of the squares
of their diameters.11
The astronomical observations and hypotheses
a) that the earth is a sphere, conjectured by both Anaxagoras and Pythagoras, and
b) that the Morning Star is the Evening Star.12
Summing up the scope of these and other advances, the
distinguished historian of Greek mathematics Sir Thomas
Heath estimates that
there is . . . probably little in the whole compass of the
Elements of Euclid, except the new theory of proportions due to Eudoxus . . . , which was not in substance
included in the recognized content of geometry and
arithmetic by Plato’s time.13
Eudoxus (born 395–390, died 342–337) knew of Plato’s
Academy, which opened in 387, as a young man, and, after
first establishing his own distinguished school of mathematics elsewhere, he moved it to the Academy, where he is
credited with solving the proportion problem mentioned
by Heath, (probably) prior to Plato’s death in 347. Thus
Plato and the Academy had essentially all the results that
would later be systematized in 300 BCE by Euclid’s Elements, the most influential work in ancient mathematics.
In Plato’s Academy philosophy and mathematics were
seen not as independent disciplines, but as intimately related inquiries contributing to one another. The first European university, the Academy educated students in a
curriculum that proceeded through arithmetic (number
theory), geometry, stereometry (the measurement of solid
6
CHAPTER 1
bodies), and astronomy (the discovery of the mathematical properties of the heavens), before culminating in philosophy, or “dialectic” (reasoned philosophical argument).
Thus, the words inscribed above its doors are reputed to
have been “Let no one destitute of geometry enter my
doors.”14 According to Heath, Plato was right to find the
genius of the spectacular achievements of ancient Greek
mathematics in their connection to philosophy. Speaking
of those achievements, Heath asks, “How did this all come
about? What special aptitude had the Greeks for mathematics?” He answers,
The answer to this question is that their genius for mathematics was simply one aspect of their genius for philosophy. Their mathematics indeed constituted a large
part of their philosophy down to Plato. Both had the
same origin.15
Rigor and precision were the origins of Greek mathematics and Platonic philosophy. Nothing is more characteristic of that philosophy than the search for definition.
When Socrates asks What is goodness, beauty, truth, knowledge, virtue, piety, or happiness?, he is asking for definitions
of the Greek words we would roughly translate as ‘good’,
‘beauty’, ‘truth’, ‘knowledge’, ‘piety’, and ‘happiness’. Let
us use the term concepts, as it is often used in philosophy,
for the meanings that abstract nouns and noun phrases like
these share with their translations in other languages—the
realities they are used to talk about.
Confessing not to know the proper definitions of these
words/concepts, Socrates asks his interlocutors for help,
and they typically offer examples—of good things, pious
practices, and virtuous individuals. But Socrates doesn’t
want examples; he wants to know what goodness, piety,
and virtue really are. To know this is to know the real
DAW N O f W E S T E R N P H I L O S O P H Y
7
properties we attribute to something when we call it good,
pious, or virtuous. Consider another case. Suppose we ask
What is a circle? and someone answers by showing us a single
circular figure, saying That’s a circle. We would respond:
We don’t want an example of a circle; we want to know what
it is for any conceivable thing to be a circle: what conditions it
must satisfy to be a circle. The answer we seek is a definition:
A circle is the set of all points in a plane equidistant from a single
central point.
The definitions Socrates sought were similar—definitions
that give necessary and sufficient conditions for any person
or thing to be good, pious, or happy, for any statement to
be true or known to be true by someone, or for anything
to be beautiful. The goal of the joint Socratic and Platonic
enterprise was to extend the objectivity and precision of
Greek mathematics to the study of all reality. Just as stunning mathematical discoveries required concepts that were
precisely defined (like circularity) or rigorously governed by
axioms (like point), so the advances in knowledge of the
world, and of ourselves, that Socrates and Plato hoped to
achieve required precise, well-regulated concepts.
For Plato, this quest for knowledge rested on Platonic
forms, which, he believed, were the precisely delineated
concepts needed for knowledge in any domain. They
include:
(i) the forms goodness, justice, knowledge, virtue, and happiness needed for general laws explaining human behavior, human nature, and human institutions;
(ii) forms for identity and distinctness, forms for different
kinds and properties of natural numbers, forms for
two-dimensional geometrical shapes (circularity, triangularity, etc.) and their properties (area, circumference,
etc.), and forms for three-dimensional geometrical figures (sphere, cone, etc.) and their properties (volume,
8
CHAPTER 1
surface area, etc.), needed to state timeless mathematical truths;
(iii) forms for body, space, velocity, motion, rest, proportion,
weight, dimension, etc. needed to describe aspects of
the natural environment.
Plato’s goal was to use these concepts to construct general, exceptionless laws about ourselves and the cosmos,
the truth of which would be knowable, yet independent
of the knower.
It is telling that the Greek word Plato used for these concepts is translatable as “shape,” as well as “form,” indicating the role in his thinking of geometry, which was well
understood in the Academy. Just as there is such a thing
as the precisely defined form/concept circularity, which is
neither itself circular nor located at any distance from anything else, so there is such a thing as the precisely delimited form/concept beauty, which is neither itself beautiful
nor perceptible through the senses. The same is true of
the other forms. Although they are real—there are, after
all, such things as circularity, truth, and beauty -–to ask
where they are in space and how long they have been there
seems misplaced. Since Plato took them to be constituents
of the objective truths about reality which, with proper
study, we may come to know, they had to be independent
of our minds. For him, this meant that they were real things
existing outside of space and time, yet capable of being
recognized by the intellect.
These abstract concepts needed to state general explanatory truths were half of the Platonic equation. Objective
knowledge requires not only propositions to be known but
also a mind capable of knowing them. What is this mind,
or psyche, that it may know itself and the world? Havelock addresses the question, as it confronted Socrates and
Plato.16
DAW N O f W E S T E R N P H I L O S O P H Y
9
[T]owards the end of the fifth century before Christ
[about the time of Plato’s birth], it became possible for
a few Greeks to talk about their ‘souls’ as though they
had selves or personalities which were autonomous and
not fragments . . . of a cosmic life force. . . . Scholarship
has tended to connect this discovery with the life and
teaching of Socrates and to identify it with a radical
change which he introduced into the meaning of the
Greek word psyche. . . . Instead of signifying a man’s
ghost or wraith . . . a thing devoid of sense and selfconsciousness, it came to mean “the ghost that thinks,”
that is capable both of moral decision and of scientific
cognition, and is the seat of moral responsibility, something infinitely precious, an essence unique in the whole
realm of nature.17
Plato outlines his conception of the soul in Book IV of
the Republic, where he distinguishes three of its aspects or
parts—the appetites or desires, willpower or emotive force,
and reason. Proper education trains the will to be the ally
of reason. Reason then controls desire, the soul is unified,
and the agent achieves self-mastery. Plato speaks of this condition of the soul, in which each of its parts plays its proper
role, as one of justice between the parts, drawing an analogy
with the ideal state in which the philosopher king (reason)
makes decisions for the good of all that are enforced by
guardians (the will) to ensure proper order among the selfinterested citizens (the desires). In Book VII he describes
the education of philosophers in which they acquire abstract
theoretical knowledge, which requires understanding the
concepts that make such knowledge possible. To achieve
such understanding, they must turn their attention to
the forms, which are innately available to everyone.
The aim of Plato’s Academy was to provide the education that leads to this self-realization. It did this by taking
10
CHAPTER 1
students through a rigorous curriculum in logic, mathematics, and philosophy, designed to enable them “to define
the aims of human life in scientific terms and to carry them
out in a society which has been reorganized upon scientific
lines.”18 In bringing this educational plan to fruition, Plato
invented the idea of a liberal education and founded the
first institution dedicated to providing it.
Plato’s greatest student, Aristotle (384–322/1 BCE),
moved to Athens from his home in Stagira (in Thrace)
in 368/7, joining the Academy at age 17. He remained
there for twenty years, first as Plato’s student and then as
his colleague, until Plato died in 347. At that point, Plato’s
nephew became the head of the Academy and Aristotle left
to found a branch of the Academy in Assos. In 343/42, he
relocated to Macedonia, where he took over the education
of a thirteen-year-old later known as Alexander the Great.
Leaving his post when Alexander ascended the throne in
336/35, Aristotle returned to Athens a year later, where he
founded his own “Peripatetic” school, in competition with
the Academy.19 There he remained until two years before his
death.
A prodigious worker, Aristotle produced an enormous
volume of work that began in the Academy, continued in
Assos, and reached its zenith at his Peripatetic School. His
writings extended nearly every domain of human learning.
They are organized around the following major topics:
Logic and Language (including definitions of truth and
falsity, their bearers, the nature of judgment, predication,
generality, patterns of logically valid argument, and fallacies), Epistemology (including proof, knowledge, and deductive and inductive reasoning), Metaphysics (including
substance, essence, accident, existence, and God), Physics
(the natural world and the cosmos), Biology (including the
history, generation, life, and death of animals), Psychology
(including perception, memory, reasoning, sleeping, and
DAW N O f W E S T E R N P H I L O S O P H Y
11
dreaming), and Ethics, Politics, and Aesthetics (including rhetoric and poetics).
A close follower of Plato in his early days, Aristotle then
believed in the immortality of the soul, its preexistence before birth when it was acquainted with Platonic forms, and
the need in later life to recollect or rediscover the forms
through philosophical argument.20 In time, he gave up those
views and modified the theory of the forms in a far-reaching
way. He also produced the first systematic codification
of principles of logically valid inference and developed
theories of ethics and politics that were more realistic and
widely applicable than Plato’s. Finally, he began to make
good on the implicit Platonic promise of advancing empirical knowledge of the physical world and our place in it.
While it was Plato who, more than anyone else, provided
the inspiration, conceptual foundations, and institutional
framework to advance human knowledge, it was Aristotle
who, more than anyone else, gave us the systematic beginnings of logic, physics, biology, and social science (including psychology and political science).
None of the steps that Aristotle took away from his
teacher on fundamental philosophical matters was more
important than his modification of Plato’s theory of the
forms. To paraphrase what I noted earlier, it is plausible
to suppose that just as there is such a thing as the form/
concept humanity, which is neither itself human nor something of any height or weight, so there is such a thing as
the form/concept redness, which is neither itself red nor
any other color. Although it is plausible that humanity and
redness are real, it seems strange to ask where they are in
space and how long they have been there. However, Plato’s
conclusion—that the forms exist outside of space and time,
and so are eternal and unchanging, despite being accessible
to the mind—isn’t the only way to think about them. Perhaps it sounds strange to ask when and where they are
12
CHAPTER 1
because they don’t exist at any single place or time, but do
exist at many places and times—namely, at all and only the
places and times at which humans and red things do. If so,
they are contingent existents of our world just as we are.
That is how Aristotle thought of them.21
This modification of Platonic doctrine brought with it a
new metaphysics of form, matter, substance, essence, and
accident, which Aristotle used in studying physical change.
Consider an individual man, Socrates, and a particular
mountain, Mount Vesuvius. Both came into being at a
certain time, endured through many changes, and at some
point ceased, or will cease, existing. As a baby Socrates was
small, and couldn’t walk, talk, or survive on his own. In
time, he grew larger and learned to do these things, while
acquiring many new properties and losing others. One
property he never lost was being human, which was essential to his nature. In contrast to this property, which is an
essential property of everything that has it, the properties
Socrates once lacked but later acquired, as well as those he
once had but later lost, were inessential, or “accidental.” A
similar story could be told about Mount Vesuvius. It, too,
has essential properties, including being a mountain, that it
can’t exist without having, as well as accidental properties
that can be acquired or lost without affecting its continued
existence.
Aristotl
