The Complete Aristotle (eng.)

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