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consists of a term only, try it as they may, clearly do not render the
definition of the thing in question, because a definition is always a
phrase of a certain kind. One may, however, use the word 'definitory'
also of such a remark as 'The "becoming" is "beautiful"', and likewise
also of the question, 'Are sensation and knowledge the same or
different?', for argument about definitions is mostly concerned with
questions of sameness and difference. In a word we may call
'definitory' everything that falls under the same branch of inquiry as
definitions; and that all the above-mentioned examples are of this
character is clear on the face of them. For if we are able to argue
that two things are the same or are different, we shall be well
supplied by the same turn of argument with lines of attack upon their
definitions as well: for when we have shown that they are not the same
we shall have demolished the definition. Observe, please, that the
converse of this last statement does not hold: for to show that they
are the same is not enough to establish a definition. To show,
however, that they are not the same is enough of itself to overthrow
it.
A 'property' is a predicate which does not indicate the essence of a
thing, but yet belongs to that thing alone, and is predicated
convertibly of it. Thus it is a property of man to-be-capable of
learning grammar: for if A be a man, then he is capable of learning
grammar, and if he be capable of learning grammar, he is a man. For no
one calls anything a 'property' which may possibly belong to something
else, e.g. 'sleep' in the case of man, even though at a certain time
it may happen to belong to him alone. That is to say, if any such
thing were actually to be called a property, it will be called not a
'property' absolutely, but a 'temporary' or a 'relative' property: for
'being on the right hand side' is a temporary property, while
'two-footed' is in point of fact ascribed as a property in certain
relations; e.g. it is a property of man relatively to a horse and a
dog. That nothing which may belong to anything else than A is a
convertible predicate of A is clear: for it does not necessarily
follow that if something is asleep it is a man.
A 'genus' is what is predicated in the category of essence of a number
of things exhibiting differences in kind. We should treat as
predicates in the category of essence all such things as it would be
appropriate to mention in reply to the question, 'What is the object
before you?'; as, for example, in the case of man, if asked that
question, it is appropriate to say 'He is an animal'. The question,
'Is one thing in the same genus as another or in a different one?' is
also a 'generic' question; for a question of that kind as well falls
under the same branch of inquiry as the genus: for having argued that
'animal' is the genus of man, and likewise also of ox, we shall have
argued that they are in the same genus; whereas if we show that it is
the genus of the one but not of the other, we shall have argued that
these things are not in the same genus.
An 'accident' is (i) something which, though it is none of the
foregoing-i.e. neither a definition nor a property nor a genus yet
belongs to the thing: (something which may possibly either belong or
not belong to any one and the self-same thing, as (e.g.) the 'sitting
posture' may belong or not belong to some self-same thing. Likewise
also 'whiteness', for there is nothing to prevent the same thing being
at one time white, and at another not white. Of the definitions of
accident the second is the better: for if he adopts the first, any one
is bound, if he is to understand it, to know already what 'definition'
and 'genus' and 'property' are, whereas the second is sufficient of
itself to tell us the essential meaning of the term in question. To
Accident are to be attached also all comparisons of things together,
when expressed in language that is drawn in any kind of way from what
happens (accidit) to be true of them; such as, for example, the
question, 'Is the honourable or the expedient preferable?' and 'Is the
life of virtue or the life of self-indulgence the pleasanter?', and
any other problem which may happen to be phrased in terms like these.