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