Dr William

In this file, we shall look
at the

work of Aristotle.  We can not hope to cover the whole of this

which covered numerous topics ranging from political theory to

rather we shall focus on his metaphysical theories and especially in the

manner in which we might contrast them to Plato’s.  In one sense,

we might say that Aristotle and Plato offer us the two alternatives of

Greek philosophy, rationalism and empiricism.  Though we do need to

be careful here since these are terms that are introduced later into

and would not have been known by Aristotle himself. It is said that

is a rationalist who arrives at his metaphysical doctrines through the

pure application of reason, whereas Aristotle is the dogged empiricist

who arrives at his ideas through observation and research.  This at

least has been the view that has been handed down to us by a long

It is obvious that
Aristotle does

depart from Plato’s theory of forms, but it vastly underestimates the

of this metaphysics by labelling it empiricist as opposed to Plato’s

In this lecture, we shall look at one of Aristotle’s criticisms of

theory of the forms, and then at three aspects of his own metaphysics,

the notion of substance, which is the heart of this metaphysics, the

types of causality, and the distinction between potentiality and

Plato has, as we have seen,
a basic

insight that knowledge of the world cannot be simple based on the

of individual things, but requires, at least to the extent that we can

claim true knowledge of things, as opposed to mere doxa, the

of concepts or universals.  Thus, to understand this or that

thing, I must possess the concept of this thing in general.  To

the box as a box, I must understand the meaning of the word ‘box’. 

What is strange in Plato’s theory is that this universal box is a

existing entity, though of course not a sensible entity, for then it

be an individual thing, but a mental entity which he called an Idea,

pre-exists this or that individual box, and gives to this or that

box its essential nature.  Now it is the separateness of the

from the particular that Aristotle rejects.  What we know is the

and we know this world through experience.  What we know through

are individual things and it is in knowing these individual things that

we come to know what universal are.  Universals are merely what is

common to individual things, and therefore cannot be said to have an

existence from these individual things.  I know what the universal

‘box’ means, because I have come across many boxes in my experience and

have noticed that these boxes all have something in common which can be

named by the word box, but this does not prove at all that something

box exists, even as a mental entity.

The fact that all that
exists for

Aristotle are individual things is further underlined in his theory of

substance.  The idea of substance, or ousia in Greek, is

cornerstone of Aristotle’s thought, just as the theory of forms is the

cornerstone of Plato’s thought.  Aristotle first arrives at a

of substance in a work called the Categories.  The subject

matter of this work is the possible predicates of an object. 

is not interested about what can be predicated of an object individual,

this wall is white, for there would be many predicates like these as

would be objects, but what can be predicated of objects in

Another way of thinking about this is that you can see the difference

thinking about the properties of different objects from the properties

that every object must have to be an object at all.  Aristotle

that there were 10 such categories:

1) what

2) how much - quantity

3) of what kind - quality

4) related to what  -

5) where - place

6) when - time

7) rest - position

8) have - state or condition

9) to do active - Action

10) to suffer passive -

 The most important of

categories is that of substance, for substance is the primary mode of

for Aristotle, for science and philosophy talks about ‘what is’ first of

all, and only then about the other nine categories (in fact in the Metaphysics,

Aristotle will say that the topic of ‘first philosophy’, by which he

the discussion of basic principles, is the question of the ‘what is’ or

the question of being).  The examples of substance Aristotle gives

in the list of categories is ‘man’ and ‘horse’.  Now these examples

of are like Platonic forms in that they are universal.  Is this

Aristotle thought primarily what ‘what is’ is, a network of forms or

But this would make him too much of a Platonist.  In fact what is

real for Aristotle are not universals but individuals.  ‘Man’ and

‘horse’ for Aristotle are only secondary substances. What are primary
substances are individual things such as this man called Socrates or
brown horse.  From a logical point of view, we can say that a
for Aristotle is something that can be a subject of a predicate. 
This is why substance is primary, for it is that thing to which are
predicates.  In this sense universals are secondary for Aristotle
because they only have a meaning when attached to or predicated of
things, but cannot be said to have any existence separate of these
things.  I predicate ‘man’ of Socrates, but it is Socrates who
and not man in general [1]

 The relation to a
subject and

individual things also allows Aristotle to explain change in the

world.  With Aristotle change or ‘becoming’ again becomes central

to philosophy, and is not rejected for the timeless nature of

In fact being itself is understood as becoming, for what is is now

as individual things which undergo change, rather than as universal

which are fixed for all time and impose unity and order on individual

which are downgraded to mere copies.  How does Aristotle understand

change?  He understands it through the basic opposition of

and actuality.  Something that exists can change into something

it was not previously.  A can change to B.  Aristotle argues

that A cannot change to B if it does not in some sense contain B within

in.  Thus in nature there is no sudden change from one state to the

next.  Thus we say that B is potentially in A, or that A actualises

its potential B when it actualises itself in the state B.  But

theory of potentiality and actuality is slightly more complex than

For he says that an actuality is always prior to a potentiality. 

A is not potentiality B unless it can come actually to be B, if A can

be B then it cannot be said to have the potentiality of being B. 

But something cannot come to be from a potential, something actual must

cause it to move from A to B.  Thus the acorn has the potential to

become an actual oak tree, but only because there is a cause, whether

or internal which leads it to this development.  This leads us to

Aristotle’s theory of causation.

We might say that the
question of

substance tells us what something is, whereas the question of cause

why something is what it is.  For Aristotle, there are four kinds

of cause that he names as follows: material cause, efficient

, formal cause, and final cause.  All

different kinds of cause tell why something is the kind of thing that it

is, and not some other kind of thing.  Cause here means types of

and should not be confused with the modern conception of cause that

a notion of one body effecting another body.  The Aristotelian

of cause is not the same as the cause and effect.  Let us briefly

then describe the different types of cause in Aristotle.

The material cause is that
by which

something is made, it

s matter so to speak.  The

formal cause is that by which this matter is formed into some particular

thing.  It is that by which shapeless matter becomes a particular

individual thing distinct from other particular things, or sharing the

same properties with those things which belong to the same set. 

efficient cause is that by which sets in motion the initial development

by which matter is determined by a particular form.  The final

is the end of this process of development by which something becomes

it is.  In other words the final cause is the realisation of the


Perhaps the best way to
think about

the difference meanings of cause in Aristotle is to use an

Suppose we ask ourselves why is it that there is an oak tree growing

of our window.  There must be a seed from which the oak tree has

which has the potential to become an oak tree, this is the material

The oak tree must have followed a definite path of development which is

belongs to the essence of oak trees, this is the formal cause.  The

seed of the oak had an origin, which was the parent oak tree, this is

efficient cause, and finally there is a final stage where the

of the oak reaches its proper realisation, this is the final cause of

oak tree.

This is only a brief
summary of the

main element of Aristotle’s philosophy, and it in no way captures the

For example, we have said nothing about his theology that had an

effect on the development of Christian thought, nor his theory of

What we can say about Aristotle, however, is that for the first time, in

Greek philosophy, we have a systematic philosophy, and it is perhaps

that is the most important legacy of his thought.


[1] It can be argued
the nature

of substance in the Metaphysics is not the same as the

of substance in the Categories.  In a more substantial

this difference would need to be investigated.


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