International Catholic University
Substance, we have seen, is the principal concern of metaphysics: its sufficient subject.
The subject of metaphysics is defined without matter and motion.
So we might expect that what we will be given is an account or definition of substance that excludes matter and motion.
But that is not what happens. When Aristotle and Thomas begin to talk of substance and essence, they dwell on physical substance, the essence of material things. Why is this?
We name things as we know them. If there is a trajectory of our knowledge from sensible things to more than sensible things, it is well to rehearse this trajectory
We will know what we mean by substance your court on an analogy with what we mean by substance in its most obvious and accessible meaning, sensible substance
The three principles of motion. Wood that is lacking the shape of Socrates comes to have that shape thanks to the sculptor. A subject -- hyle -- which has a lack -- steresis -- of the form -- morphe -- that it acquires in the change.
The subject of the change is that to which the motion is attributed and which survives the change.
The privation is replaced by the form
The result of the change is a compound of matter and form.
Substantial change -- prime matter, substantial form
"Therefore if the form is prior to the matter and more real, it will be prior also to the compound of both, for the same reason." -- Aristotle
In the physical thing, its actuality, that which makes it to be and be what it is, is "more" substance than is the matter, the potential principle . . .
To describe a statue as wood is less informative than to describe it as Socrates. In the latter case, we draw attention to form, to what makes it to be what it is . . .
This is true of the incidental properties of a thing; it is also true of substantial form.
In the case of the human soul, we have a substantial form which is capable of existing without a body -- it is a quasi-substance . . . this is not what the human soul is, something that exists apart from body, as if that were its standard or usual status . . . so we call it a quasi-susbtance
If on the other hand there are substances which exist apart from matter always and in the nature of the case, they are subsistent forms
"It is evident that the essence of man differs from the essence of Socrates only as the designated differs from the non-designated." -- Thomas Aquinas
Plato -- that which a thing is, its essence, exists independently of and apart from the thing whose essence it is
Aristotle rejects this
It seems self evident that a thing and what it is should be one.
But are they in every sense the same? The essence of Socrates is what-it-is-to-be-a-man, humanity. But can we say that Socrates is humanity? Socrates and Plato would then have to be the same man.
So a thing and its essence cannot be the same when there are many individuals of the same kind.
If there are things which are in every way one with their essence, they will be more essence or substance than material things
"The notion of species is not among the things that belong to the nature according to its absolute consideration, nor is it among the accidents which follow on the existence it has outside the soul, like whiteness and blackness; rather it is among the accidents that follow on it according to the existence it has in intellect." -- Thomas Aquinas
Porphyry and the problem of universals
Genus, species, property, difference, accident
The predicates of 2 and 3 are true per accidens or incidentally; they are not part of the definition of the thing of which they are said . . . they befall it because in [2] some individual man happens to be seated, and in the case of [3] because of the existence of the nature in the human mind
Universality is an incidental property of the nature as known by us . . . something one that is said of many
Universals in this sense are not causes
Universal causes are individual things whose causality extends to many effects . . .