Raphael’s School of Athens depicts Aristotle and Plato at the
center of a group of ancient Greek philosophers modeled on Raphael’s
contemporaries. Plato’s finger points upward, while Aristotle’s hand is
held at waist height, stretched out toward the ground. The image captures
the major philosophical difference between the two great thinkers of
antiquity: While Plato thought that real things (what he called the
“forms”) lie outside our experience, Aristotle believed that real things
(which he called “substances”) are in the everyday world around us. This is
why so much of Aristotle’s work covers topics which would now be the
subject of empirical science (animal biology, the weather, and so on). With
his commitment to the reality of the ordinary things we experience and his
tireless need to classify and taxonomize, Aristotle was in some ways the
first systematic scientist of the Western world.
Aristotle’s view that substances are the fundamental realities was put
forward in his difficult and influential work known as the Metaphysics. We owe the term “metaphysics” itself to Aristotle,
though in a rather indirect way. When his works were collected in the
edition made by Andronicus of Rhodes in the first century b.c., the
writings dealing with substance and causation were placed after his theory
of nature, which appeared in the book known as the Physics (from
the Greek word for nature, phusis). Hence, the work was described
as “what comes after the Physics,” from which we derive our word metaphysics. Yet this word has something of a philosophical
justification, too, for while Aristotle’s Physics deals with
questions about time and change, the Metaphysics goes further
(“after physics,” as it were) and asks about being as such.
What does it mean for anything to be?
What does it mean for anything to be?
Aristotle approaches this question by describing the nature of the most
fundamental beings, those he called “primary substances.” His paradigm of a
substance is an organism: an individual horse or human being. It is
crucial, then, that Aristotle’s word “substance” does not mean “stuff” (as
in “tar is a thick, black, viscous substance”). It means, rather, a
fundamental being.
Primary substances are characterized by their essences. All beings can be
classified in terms of genera and species: Thus, human beings are of the
genus animal, and the species rational. It is of the
essence of human beings in general, then, to be rational animals. But what
is it to be a primary or individual substance—say, an individual human
being? Aristotle argued that each individual substance was a kind of
compound, made of matter organized in a certain way. The way in which
something is organized he called its form. This is known as the
“hylomorphic” view of substance, from the Greek hyle (matter) and morphe (form).
The form of an individual substance is the essence of the kind of
substance, exemplified in an individual member of that kind. This is the
crucial difference between the Aristotelian and Platonic conceptions of
form. For Plato, the ordinary things we see around us are in some way
imperfect versions of the real forms which lie outside experience. The
forms are not in the objects themselves; if anything, the objects
approximate to their forms. Individual horses approximate to, or
participate in, or imperfectly resemble the “form of the horse.”
This is the first of your three free articles for the month.
For Aristotle, by contrast, the form of a substance is in the substance
itself (in traditional terminology, it is immanent, rather than
transcendent). Moreover, the form explains the characteristic activity of a
substance, as being in accordance with what it is ultimately for:
The form is the principle that governs the activity of a substance, that
which explains why a substance does what it does. The goal of a human
being, for example, is to live a life of rational activity; something
having the essence of a rational animal will strive toward this goal. Thus
Aristotle’s theory of substance is sometimes called a “teleological”
theory: It describes a substance in terms of its characteristic goal (telos in Greek).
It is a commonplace of the history of science and philosophy that this
Aristotelian philosophy—which dominated the academic (or scholastic)
philosophy of the Middle Ages in the monasteries and universities of
Europe—was overthrown by the Scientific Revolution of the sixteenth and
seventeenth centuries, a revolution embodied in the works of Galileo,
Francis Bacon, and René Descartes. Scholastics had thought of everything in
the world as having purposes and goals. The new philosophers of the
Scientific Revolution conceived the world instead in terms of
mathematically measurable mechanisms. Galileo famously spoke of “this grand
book the universe, which . . . is written in the language of mathematics,
and its characters are triangles, circles, and other geometric figures,
without which it is humanly impossible to understand a single word of it.”
The new mathematical or “mechanical” philosophy scorned the Aristotelian
philosophy of the scholastic period. Francis Bacon said that Aristotle
“made his natural philosophy a mere bond-servant to his logic, thereby
rendering it contentious and well nigh useless.” In other words, his
philosophy of nature was a priori (prior to experience) and based
purely on the concepts of things derived from logical classification.
Despite misrepresenting Aristotle’s own dedication to empirical inquiry,
this kind of criticism stuck. In the wider culture, the rejection of
scholasticism was immortalized by the remark of the doctor in Molière’s
play The Hypochondriac, that opium puts us to sleep because it has
a “dormitive virtue” (virtus dormitiva).
This customary story of the Scientific Revolution and its rejection of Aristotelian scholasticism is incomplete and inaccurate in many ways. Not all great philosophers of the period rejected Aristotelian thinking in its entirety. Gottfried Wilhelm Leibniz (1646–1716) criticized scholastic philosophers who “believed they could explain the properties of bodies by referring to forms and qualities, without taking the trouble to find out how they worked: as if we were happy to say that a clock has a time-indicative quality deriving from its form, without considering what all that amounted to.” But despite this criticism, Leibniz said that Aristotelian substantial forms “are not so far from the truth, nor so ridiculous, as the common run of our new philosophers suppose.” Substance and form could be used to explain the ultimate nature of things, Leibniz believed, even if they are not needed to explain ordinary, everyday things, like the time-keeping properties of clocks. It is also important to remember that within the Catholic intellectual tradition, Aristotelian ideas continued to be taught in universities and seminaries for centuries after the Scientific Revolution.
Nonetheless, Aristotelian metaphysics was largely absent from what might be
called (with apologies to the seminaries) mainstream philosophy from
Descartes to the present day. Metaphysics took various forms between then
and now, but almost none of it involved Aristotelian notions of telos, form, or substance. The history of philosophy in the
twentieth century is instructive. In English-speaking (“analytic”)
philosophy, the attitude to metaphysics—that is, to abstract,
non-scientific, or non-empirical speculation about the nature of
reality—was dominated by the critique of the logical positivists of the
pre–World War II Vienna Circle. These philosophers proposed that
verifiability by empirical science was the measure of meaningfulness for
claims about the world. Metaphysical claims—including but not limited to
traditional Aristotelian claims about substance, essence, form, and so
on—would be examples of the unverifiable. Metaphysics was dismissed as
outdated pseudoscience.
Some logical positivists traced their inspiration from the philosophy of
David Hume (1711–1776), who had proposed a division of claims into those
that are “matters of fact” and those that involve only “relations of
ideas.” Ordinary empirical claims are in the first category, while
mathematics and logic are in the second. If some inquiry—Hume famously took
“divinity or school metaphysics” as an example—fits into neither category,
then his advice was to “commit it then to the flames: for it can contain
nothing but sophistry and illusion.” This sums up the logical positivists’
approach to metaphysics (and theology, for that matter).
Nonetheless, Hume had a metaphysics of his own—a rather austere one, but a
metaphysics nonetheless. His metaphysics denied that there was any necessity in reality at all: Things happen as they do not because
of any necessity or essence or ultimate reason, but because they just do.
The world is a regular place; things happen in generally unsurprising ways;
but this is not an indication of any deeper necessity in nature.
Causation—what Hume called “the cement of the Universe”—is just a matter of
the “constant conjunction” of things of similar kinds: Smoke always follows
fire, and so on. Defenders of Hume’s metaphysics called the summaries of
these regularities “laws” and interpreted scientific laws as
generalizations of this kind. With the demise of logical positivism in the
1950s and ’60s, Humean theories of cause and law became the foundations of
metaphysics in analytic philosophy. Indeed, if you had left the world of
philosophy in the 1970s, you might have thought that Humean, empiricist,
science-based metaphysics was the only metaphysics worth taking seriously.
Things did not stay like this, however. Aristotelian metaphysics started to
return, and the volume under review is one of many books that have come out
in recent years defending Aristotelian views of causation, substance,
attribute, and even essence and form. How did this change come about? And
how can Aristotelian metaphysics—which, if the standard history is to be
believed, was rejected on the basis of discoveries of modern science—be
part of a serious, scientific worldview? How can serious thinkers propose
“neo-Aristotelian perspectives” on contemporary science? John Haldane, in
the preface to Neo-Aristotelian Perspectives, poses the challenge
by asking why this project isn’t like “astrological perspectives on
astronomy.”
The first factor in the rebirth of Aristotelianism came from an unexpected
place: formal logic, in particular the logical theories developed in the
1960s and ’70s by Saul Kripke, one of the great philosophers of the late
twentieth century. A teenage prodigy, Kripke developed a way to understand
the logic of possibility and necessity (so-called “modal logics”), which
led to certain natural metaphysical interpretations. Philosophers had
talked for some time in terms of necessary truth as truth in all possible
worlds. Kripke introduced a precise way of formulating this idea, and
pursued its interpretation into a metaphysics of essence and necessity. One
central idea was that if we want to make sense when we say that something
is necessarily such and such (for example, that a person is necessarily
human), we should think of this as a feature that it has in all possible
worlds in which it exists. But if this is the right way to think, then we
must also be able to identify the same individual in these different
possible worlds. And in order to do this, there must be something about it
which makes it the individual it is in each of the worlds in which it
exists. And what is this but its essence?
Kripke extended the idea of essence beyond individuals to kinds of things,
such as gold and water. We can imagine that gold might have a slightly
different color, for example, but what makes it the case that it is gold we are imagining, rather than something that is rather like
gold in certain respects? Kripke argued that to identify gold in different
possible situations requires that gold have an essence. He proposed that
the essence of an element is its atomic number, so gold is essentially the
element with the atomic number 79. The details do not matter here; what was
important was the idea that the world has a natural order, an order which
is neither imposed by our interpretation nor just the order of Humean laws
of nature. Human beings discovered that water is H2O; we did not
invent this fact. What we were discovering, Kripke and his followers
argued, is not just a law or regularity: It is rather the essence of the
natural kind water. These ideas are clearly Aristotelian in inspiration.
Essences are, of course, anathema to Humean metaphysics and to the
post-positivist philosophy of W. V. Quine and his followers (Quine himself said that Aristotle’s
distinction between essence and accident is “surely indefensible”). But
armed with Kripke’s logical and metaphysical framework, people could defend
essence against the Quinean critique. More recently, self-identified
Aristotelians such as Kit Fine have argued that the natural order of the
world requires that certain things are more fundamental than others, and
that fundamental things stand in a relation to non-fundamental things that
can be called “grounding.” For example, the United Nations genuinely
exists; it is an entity, but no one would claim it is a fundamental entity.
The United Nations is made up of entities, nations, which perhaps have more
of a claim to be real, and these things themselves are made up of entities,
human beings, which an Aristotelian would call substances. It is asserted
that the less fundamental entities can be grounded in the being and
activity of more fundamental entities. (In the volume under review, Robert
Koons discusses grounding in the context of an Aristotelian philosophy of
physics.) 
The second area of philosophy in which Aristotelian ideas has returned is
the philosophy of causation (or causality): the study of cause and effect.
According to Hume’s influential conception of causation, “all events seem
to be entirely loose and separate.” There is no necessary connection
between distinct existences. Yet Humeans always had trouble with causal
relations that were a result of so-called “dispositional” properties:
solubility, fragility, and so on. These are properties that are described
in terms of the effects that their possession is “disposed” to bring
about—dissolving, breaking, etc. How can all events be “loose and separate”
if some events (such as dissolving) seem to be essentially or
metaphysically connected to their causes (solubility)?
Humeans have responded by arguing that such dispositionality is not a real
feature of the world, but only an artifact of our description of it. What
causes dissolving is the interaction between certain events (being put in
water, say) and the “structural” or “categorical” properties of things
(molecular structure, and so on). And these interactions are covered by
laws of nature, as per the usual Humean theory of causation. Defenders of
dispositions push back against this: How do we actually specify these
supposed “structural” properties? Isn’t structure partly characterized in
dispositional terms (for example, in terms of the ability to resist
pressure at various points)?
This line of thought can be supported by looking closely at what the laws
of nature actually say. Many laws of nature characterize the properties of
things in terms of the effects that an object’s having these properties
lead to. For example, Newton’s second law of motion defines the force
exerted on a body as the product of its mass and its acceleration (force
equals mass times acceleration or f=ma). Defenders of the reality
of dispositions argue that this law can be understood as a definition of
what, say, an object’s mass—one of its properties—really is: It is a disposition to accelerate under a given force, in
accord with that equation. So rather than just describing a mere regularity
between “loose and separate” existences, as the Humeans say, laws like
Newton’s should be understood as defining the nature of properties in terms
of their characteristic effects—that is, in dispositional terms.
This kind of challenge to the Humean view led to the development of
sophisticated theories of properties understood as “causal powers.” This
terminology was introduced in an influential book by Rom Harré and E. H.
Madden in 1975, and the basic idea has been developed more recently in
various ways by George Molnar (Powers, 2003), Stephen Mumford and
Rani Lill Anjum (Getting Causes from Powers, 2011), and Anna
Marmodoro (The Metaphysics of Powers, 2010). Marmodoro is one of
the recent philosophers who has brought out most explicitly the
Aristotelian roots of the powers-dispositions view of causation, linking
it to Aristotle’s famous discussions of potentiality and actuality. Her
work is well represented in the volume under review by an essay (cowritten
with Christopher Austin) linking the notion of potentiality with the
concept of the unity of an organism. In an interesting and complementary
discussion, Janice Chik Breidenbach’s essay defends the Aristotelian view
that substances themselves can be causes (it was the horse that knocked
down the gate, not just some event involving, for instance, the horse’s
legs). And Humeanism in metaphysics as a whole is discussed in William
Simpson’s essay on why dispositions cannot be fully or properly
accommodated within a Humean framework.
A third important factor in the revival of Aristotelian metaphysics comes
from the development of the philosophy of science itself. Again, the
crucial immediate historical precursors were the logical positivists and
those influenced by them. The logical positivists had seen scientific
theories as aiming at the statement of laws of nature which were as general
and exceptionless as possible. The paradigm was physics: Laws such as
Newton’s aim to state the most general truths about how the universe
behaves. According to the positivists, the fact that Newton’s laws are not
actually true should not be blamed on their claim to generality. Rather,
these philosophers looked to replace these laws with laws that were equally
general. This idea—science aims at laws, and laws should be regarded as
statements that are as general and exceptionless as possible—came under
critical scrutiny in work from the 1970s and ’80s. This work emphasized the
partial, local nature of scientific theory, the importance of modeling in
science, and the unrealistic character of the positivists’ description of
science as a list of statements of universal laws. An influential figure
here is Nancy Cartwright, who gave an alternative description of science in
terms of the measurement of “Nature’s capacities.” Rather than being
something of which one single scientific story could be told—in a “theory
of everything,” as it were—the world is, in Cartwright’s image, irreducibly
“dappled.” It is made up of a plurality of different kinds of things, about
which there is no one fundamental account, only separate accounts for
separate kinds of things and their various capacities. This is clearly an
Aristotelian picture, as Cartwright herself acknowledges, with its emphasis
on capacities (a notion closely related to that of a power or disposition)
and on things being of different kinds. In Neo-Aristotelian Perspectives, Xavi Lanao and Nicholas Teh
apply some of Cartwright’s ideas to argue that even classical mechanics
does not conform to the “fundamentalist” picture of science criticized by
Cartwright.
To these factors must be added a fourth factor, which is often not
explicitly credited as an influence on the present rebirth of
Aristotelianism: the influence of Catholic philosophy and its own resilient
metaphysics. It will not be news to readers of this journal that Catholic
seminaries and universities continued to teach Thomistic philosophy (itself
a form of Aristotelianism), and leading Thomist (or Thomism-inspired)
philosophers such as Bernard Lonergan have had a wide influence, albeit one
which rarely made contact with mainstream metaphysics in the twentieth
century. Yet the revolt against the dominant Humean metaphysics in recent
decades has led to more dialogue (and even collaboration) between Catholic
and what I am calling mainstream philosophy. The present book is a good
example. Many of the contributors are Roman Catholics—some known
independently for their work in the philosophy of religion—and some teach
at Catholic universities in the United States. Their Catholicism plays
little direct role in their actual philosophical contributions to this
volume, but it provides the intellectual framework within which many of
these thinkers work.
One way in which Thomistic metaphysics influences the rest of philosophy,
for example, is in the question of the soul and its relation to the body.
It is easy to see why this should be such an important question for
Catholics. The traditional Thomistic view, drawn from Aristotle, is
hylomorphic: The soul is the form of the body’s matter. For Aristotle, any
substance (like a human being) is a compound of form and matter; the matter
cannot exist without the form, and the form cannot exist without the
matter. In the current volume, William Jaworski gives a clear
interpretation of how this view of the human being might “leave it
unmysterious how thought, feeling and perception can exist in the natural
world.” Another important area where contemporary hylomorphists apply their
ideas is the philosophy of biology, exemplified here in fine essays by
David Oderberg and Daniel De Haan.
I hope that these largely historical considerations begin to clarify why
Aristotelian philosophy (in particular, metaphysics) has returned. But I
hope they also show how Aristotelian metaphysics can be scientifically
defensible. Remember that the worry was that the Scientific Revolution of
the sixteenth and seventeenth centuries saw Aristotelian philosophy as
unscientific—in a sense, the traditional view is that science as a
systematic attempt at genuine explanation only began with the rejection of
Aristotelianism and scholasticism.
But it should be noted that these are philosophical claims, not scientific
ones. Like the positivists’ claim that only what can be verified can be
genuinely meaningful, or the “scientistic” claim that science can explain
everything, these are not claims made within scientific theories
themselves. Indeed, metaphysical claims—about substance, cause, change,
potentiality, etc.—are very rarely settled by the content of scientific
theories. If you are interested in how change is possible, you will not
look to physics or chemistry. Physicists and chemists presuppose that
change is possible and then go on to talk about the specific nature of
specific changes. Similarly, physics and chemistry do not settle the
question of whether the physical world is all there is; that question must
be left to metaphysics.
Although science is not itself metaphysics, metaphysics of science is
unavoidable. Once we start theorizing at a certain level of generality, we
cannot escape metaphysical commitments. For example, if we ask what kind of
entities physical theories are committed to, we may have to answer in terms
of traditional categories such as substance, property, object, process—or
specify some new categories. This does not mean that physicists must be
metaphysicians, only that if they enter into metaphysical speculation, they
should acknowledge that others have been there before them, and that the
questions are not easy. For example, in attempting to argue that a causal
connection exists between some phenomena, it is common to find scientists
saying “correlation is not causation”—and they are right. But what is
causation, then, and how does it differ from mere correlation? Answering
this requires metaphysics. Those philosophers and scientists who dismiss
metaphysics, often casually and without much argument, have to demonstrate
how they can do this without doing metaphysics themselves. I predict that
they will not be able to do this. Even the logical positivists had
metaphysical assumptions.
The lesson of this is that seventeenth-century science did not prove that
Aristotelian metaphysics failed—this was simply a claim made by
philosophers. Whether science requires specific metaphysical assumptions or
not is itself a metaphysical debate, which requires knowledge of science
but is not settled by it. Aristotelian metaphysical categories—substance,
form, capacity, essence—can be intelligibly applied to the findings of
science. Or, at least, there are no scientific arguments against this.
This is why Neo-Aristotelian Perspectives on Contemporary Science
is not analogous to neo-astrological perspectives on contemporary
astronomy.
