The Physics takes its title from the
Greek word phusis, which translates more accurately
as “the order of nature.” The first two books of the Physics are
Aristotle’s general introduction to the study of nature. The remaining
six books treat physics itself at a very theoretical, generalized
level, culminating in a discussion of God, the First Cause.
Summary
The Physics opens with an investigation
into the principles of nature. At root, there must be a certain
number of basic principles at work in nature, according to which
all natural processes can be explained. All change or process involves
something coming to be from out of its opposite. Something comes
to be what it is by acquiring its distinctive form—for example,
a baby becomes an adult, a seed becomes a mature plant, and so on.
Since this the baby or the seed were working toward this form all
along, the form itself (the idea or pattern of the mature specimen)
must have existed before the baby or seed actually matured. Thus,
the form must be one of the principles of nature. Another principle
of nature must be the privation or absence of this form, the opposite
out of which the form came into being. Besides form and privation,
there must be a third principle, matter, which remains constant
throughout the process of change. If nothing remains unchanged when
something undergoes a change, then there would be no “thing” that
we could say underwent the change. So there are three basic principles
of nature: matter, form, and privation. For example, a person’s
education involves the form of being educated, the privation of
being ignorant, and the underlying matter of the person who makes
the change from ignorance to education. This view of the principles
of nature resolves many of the problems of earlier philosophers
and suggests that matter is conserved: though its form may change,
the underlying matter involved in changes remains constant.
Change takes place according to four different kinds of
cause. These causes are closer to what we might call “explanations”:
they explain in different ways why the change came to pass. The
four causes are (1) material cause, which explains what something
is made of; (2) formal cause, which explains the form or pattern
to which a thing corresponds; (3) efficient cause, which is what
we ordinarily mean by “cause,” the original source of the change;
and (4) final cause, which is the intended purpose of the change.
For example, in the making of a house, the material cause is the
materials the house is made of, the formal cause is the architect’s
plan, the efficient cause is the process of building it, and the
final cause is to provide shelter and comfort. Natural objects,
such as plants and animals, differ from artificial objects in that
they have an internal source of change. All the causes of change
in artificial objects are found outside the objects themselves,
but natural objects can cause change from within.
Aristotle rejects the idea that chance constitutes a fifth
cause, similar in nature to the other four. We normally talk about
chance in reference to coincidences, where two separate events,
which had their own causes, coincide in a way that is not explained
by either set of causes. For instance, two people might both have
their own reasons for being in a certain place at a certain time,
but neither of these sets of reasons explains the coincidence of
both people being there at the same time.
Final causes apply to nature as much as to art, so everything
in nature serves a useful purpose. Aristotle argues against the
views both of Democritus, who thinks that necessity in nature has
no useful purpose, and of Empedocles, who holds an evolutionary
view according to which only those combinations of living parts
that are useful have managed to survive and reproduce themselves.
If Democritus were right, there would be as many useless aspects
of nature as there are useful, while Empedocles’ theory does not
explain how random combinations of parts could come together in
the first place.
Books III and IV examine some fundamental concepts of
nature, starting with change, and then treating infinity, place,
void, and time. Aristotle defines change as “the actuality of that
which exists potentially, in so far as it is potentially this actuality.”
That is, change rests in the potential of one thing to become another.
In all cases, change comes to pass through contact between an agent
and a patient, where the agent imparts its form to the patient and
the change itself takes place in the patient.
