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Categories, Section 1, Part 5

Substance, in the truest and primary and most definite sense of the
word, is that which is neither predicable of a subject nor present
in a subject; for instance, the individual man or horse. But in a
secondary sense those things are called substances within which, as
species, the primary substances are included; also those which, as
genera, include the species. For instance, the individual man is included
in the species 'man', and the genus to which the species belongs is
'animal'; these, therefore-that is to say, the species 'man' and the
genus 'animal,-are termed secondary substances.

It is plain from what has been said that both the name and the definition
of the predicate must be predicable of the subject. For instance,
'man' is predicted of the individual man. Now in this case the name
of the species man' is applied to the individual, for we use the term
'man' in describing the individual; and the definition of 'man' will
also be predicated of the individual man, for the individual man is
both man and animal. Thus, both the name and the definition of the
species are predicable of the individual.

With regard, on the other hand, to those things which are present
in a subject, it is generally the case that neither their name nor
their definition is predicable of that in which they are present.
Though, however, the definition is never predicable, there is nothing
in certain cases to prevent the name being used. For instance, 'white'
being present in a body is predicated of that in which it is present,
for a body is called white: the definition, however, of the colour
white' is never predicable of the body.

Everything except primary substances is either predicable of a primary
substance or present in a primary substance. This becomes evident
by reference to particular instances which occur. 'Animal' is predicated
of the species 'man', therefore of the individual man, for if there
were no individual man of whom it could be predicated, it could not
be predicated of the species 'man' at all. Again, colour is present
in body, therefore in individual bodies, for if there were no individual
body in which it was present, it could not be present in body at all.
Thus everything except primary substances is either predicated of
primary substances, or is present in them, and if these last did not
exist, it would be impossible for anything else to exist.

Of secondary substances, the species is more truly substance than
the genus, being more nearly related to primary substance. For if
any one should render an account of what a primary substance is, he
would render a more instructive account, and one more proper to the
subject, by stating the species than by stating the genus. Thus, he
would give a more instructive account of an individual man by stating
that he was man than by stating that he was animal, for the former
description is peculiar to the individual in a greater degree, while
the latter is too general. Again, the man who gives an account of
the nature of an individual tree will give a more instructive account
by mentioning the species 'tree' than by mentioning the genus 'plant'.

Moreover, primary substances are most properly called substances in
virtue of the fact that they are the entities which underlie every.
else, and that everything else is either predicated of them or present
in them. Now the same relation which subsists between primary substance
and everything else subsists also between the species and the genus:
for the species is to the genus as subject is to predicate, since
the genus is predicated of the species, whereas the species cannot
be predicated of the genus. Thus we have a second ground for asserting
that the species is more truly substance than the genus.

Of species themselves, except in the case of such as are genera, no
one is more truly substance than another. We should not give a more
appropriate account of the individual man by stating the species to
which he belonged, than we should of an individual horse by adopting
the same method of definition. In the same way, of primary substances,
no one is more truly substance than another; an individual man is
not more truly substance than an individual ox.

It is, then, with good reason that of all that remains, when we exclude
primary substances, we concede to species and genera alone the name
'secondary substance', for these alone of all the predicates convey
a knowledge of primary substance. For it is by stating the species
or the genus that we appropriately define any individual man; and
we shall make our definition more exact by stating the former than
by stating the latter. All other things that we state, such as that
he is white, that he runs, and so on, are irrelevant to the definition.
Thus it is just that these alone, apart from primary substances, should
be called substances.

Further, primary substances are most properly so called, because they
underlie and are the subjects of everything else. Now the same relation
that subsists between primary substance and everything else subsists
also between the species and the genus to which the primary substance
belongs, on the one hand, and every attribute which is not included
within these, on the other. For these are the subjects of all such.
If we call an individual man 'skilled in grammar', the predicate is
applicable also to the species and to the genus to which he belongs.
This law holds good in all cases.

It is a common characteristic of all sub. stance that it is never
present in a subject. For primary substance is neither present in
a subject nor predicated of a subject; while, with regard to secondary
substances, it is clear from the following arguments (apart from others)
that they are not present in a subject. For 'man' is predicated of
the individual man, but is not present in any subject: for manhood
is not present in the individual man. In the same way, 'animal' is
also predicated of the individual man, but is not present in him.
Again, when a thing is present in a subject, though the name may quite
well be applied to that in which it is present, the definition cannot
be applied. Yet of secondary substances, not only the name, but also
the definition, applies to the subject: we should use both the definition
of the species and that of the genus with reference to the individual
man. Thus substance cannot be present in a subject.

Yet this is not peculiar to substance, for it is also the case that
differentiae cannot be present in subjects. The characteristics 'terrestrial'
and 'two-footed' are predicated of the species 'man', but not present
in it. For they are not in man. Moreover, the definition of the differentia
may be predicated of that of which the differentia itself is predicated.
For instance, if the characteristic 'terrestrial' is predicated of
the species 'man', the definition also of that characteristic may
be used to form the predicate of the species 'man': for 'man' is terrestrial.

The fact that the parts of substances appear to be present in the
whole, as in a subject, should not make us apprehensive lest we should
have to admit that such parts are not substances: for in explaining
the phrase 'being present in a subject', we stated' that we meant
'otherwise than as parts in a whole'.

It is the mark of substances and of differentiae that, in all propositions
of which they form the predicate, they are predicated univocally.
For all such propositions have for their subject either the individual
or the species. It is true that, inasmuch as primary substance is
not predicable of anything, it can never form the predicate of any
proposition. But of secondary substances, the species is predicated
of the individual, the genus both of the species and of the individual.
Similarly the differentiae are predicated of the species and of the
individuals. Moreover, the definition of the species and that of the
genus are applicable to the primary substance, and that of the genus
to the species. For all that is predicated of the predicate will be
predicated also of the subject. Similarly, the definition of the differentiae
will be applicable to the species and to the individuals. But it was
stated above that the word 'univocal' was applied to those things
which had both name and definition in common. It is, therefore, established
that in every proposition, of which either substance or a differentia
forms the predicate, these are predicated univocally.

All substance appears to signify that which is individual. In the
case of primary substance this is indisputably true, for the thing
is a unit. In the case of secondary substances, when we speak, for
instance, of 'man' or 'animal', our form of speech gives the impression
that we are here also indicating that which is individual, but the
impression is not strictly true; for a secondary substance is not
an individual, but a class with a certain qualification; for it is
not one and single as a primary substance is; the words 'man', 'animal',
are predicable of more than one subject.

Yet species and genus do not merely indicate quality, like the term
'white'; 'white' indicates quality and nothing further, but species
and genus determine the quality with reference to a substance: they
signify substance qualitatively differentiated. The determinate qualification
covers a larger field in the case of the genus that in that of the
species: he who uses the word 'animal' is herein using a word of wider
extension than he who uses the word 'man'.

Another mark of substance is that it has no contrary. What could be
the contrary of any primary substance, such as the individual man
or animal? It has none. Nor can the species or the genus have a contrary.
Yet this characteristic is not peculiar to substance, but is true
of many other things, such as quantity. There is nothing that forms
the contrary of 'two cubits long' or of 'three cubits long', or of
'ten', or of any such term. A man may contend that 'much' is the contrary
of 'little', or 'great' of 'small', but of definite quantitative terms
no contrary exists.

Substance, again, does not appear to admit of variation of degree.
I do not mean by this that one substance cannot be more or less truly
substance than another, for it has already been stated' that this
is the case; but that no single substance admits of varying degrees
within itself. For instance, one particular substance, 'man', cannot
be more or less man either than himself at some other time or than
some other man. One man cannot be more man than another, as that which
is white may be more or less white than some other white object, or
as that which is beautiful may be more or less beautiful than some
other beautiful object. The same quality, moreover, is said to subsist
in a thing in varying degrees at different times. A body, being white,
is said to be whiter at one time than it was before, or, being warm,
is said to be warmer or less warm than at some other time. But substance
is not said to be more or less that which it is: a man is not more
truly a man at one time than he was before, nor is anything, if it
is substance, more or less what it is. Substance, then, does not admit
of variation of degree.

The most distinctive mark of substance appears to be that, while remaining
numerically one and the same, it is capable of admitting contrary
qualities. From among things other than substance, we should find
ourselves unable to bring forward any which possessed this mark. Thus,
one and the same colour cannot be white and black. Nor can the same
one action be good and bad: this law holds good with everything that
is not substance. But one and the selfsame substance, while retaining
its identity, is yet capable of admitting contrary qualities. The
same individual person is at one time white, at another black, at
one time warm, at another cold, at one time good, at another bad.
This capacity is found nowhere else, though it might be maintained
that a statement or opinion was an exception to the rule. The same
statement, it is agreed, can be both true and false. For if the statement
'he is sitting' is true, yet, when the person in question has risen,
the same statement will be false. The same applies to opinions. For
if any one thinks truly that a person is sitting, yet, when that person
has risen, this same opinion, if still held, will be false. Yet although
this exception may be allowed, there is, nevertheless, a difference
in the manner in which the thing takes place. It is by themselves
changing that substances admit contrary qualities. It is thus that
that which was hot becomes cold, for it has entered into a different
state. Similarly that which was white becomes black, and that which
was bad good, by a process of change; and in the same way in all other
cases it is by changing that substances are capable of admitting contrary
qualities. But statements and opinions themselves remain unaltered
in all respects: it is by the alteration in the facts of the case
that the contrary quality comes to be theirs. The statement 'he is
sitting' remains unaltered, but it is at one time true, at another
false, according to circumstances. What has been said of statements
applies also to opinions. Thus, in respect of the manner in which
the thing takes place, it is the peculiar mark of substance that it
should be capable of admitting contrary qualities; for it is by itself
changing that it does so.

If, then, a man should make this exception and contend that statements
and opinions are capable of admitting contrary qualities, his contention
is unsound. For statements and opinions are said to have this capacity,
not because they themselves undergo modification, but because this
modification occurs in the case of something else. The truth or falsity
of a statement depends on facts, and not on any power on the part
of the statement itself of admitting contrary qualities. In short,
there is nothing which can alter the nature of statements and opinions.
As, then, no change takes place in themselves, these cannot be said
to be capable of admitting contrary qualities.

But it is by reason of the modification which takes place within the
substance itself that a substance is said to be capable of admitting
contrary qualities; for a substance admits within itself either disease
or health, whiteness or blackness. It is in this sense that it is
said to be capable of admitting contrary qualities.

To sum up, it is a distinctive mark of substance, that, while remaining
numerically one and the same, it is capable of admitting contrary
qualities, the modification taking place through a change in the substance
itself.

Let these remarks suffice on the subject of substance.

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