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being musical, possesses knowledge in some respect, then also 'music'
is a particular kind of 'knowledge'; and also that if what walks is
moved in walking, then 'walking' is a particular kind of 'movement';
you should therefore examine in the aforesaid manner any genus in
which you want to establish the existence of something; e.g. if you
wish to prove that 'knowledge' is a form of 'conviction', see whether
the knower in knowing is convinced: for then clearly knowledge would
be a particular kind of conviction. You should proceed in the same way
also in regard to the other cases of this kind.
Moreover, seeing that it is difficult to distinguish whatever always
follows along with a thing, and is not convertible with it, from its
genus, if A follows B universally, whereas B does not follow A
universally-as e.g. 'rest' always follows a 'calm' and 'divisibility'
follows 'number', but not conversely (for the divisible is not always
a number, nor rest a calm)-you may yourself assume in your treatment
of them that the one which always follows is the genus, whenever the
other is not convertible with it: if, on the other hand, some one else
puts forward the proposition, do not accept it universally. An
objection to it is that 'not-being' always follows what is 'coming to
be' (for what is coming to be is not) and is not convertible with it
(for what is not is not always coming to be), and that still
'not-being' is not the genus of 'coming to be': for 'not-being' has
not any species at all. Questions, then, in regard to Genus should be
investigated in the ways described.

Topics
By Aristotle
Written 350 B.C.E Part 1
The question whether the attribute stated is or is not a property,
should be examined by the following methods:
Any 'property' rendered is always either essential and permanent or
relative and temporary: e.g. it is an 'essential property' of man to
be 'by nature a civilized animal': a 'relative property' is one like
that of the soul in relation to the body, viz. that the one is fitted
to command, and the other to obey: a 'permanent property' is one like
the property which belongs to God, of being an 'immortal living
being': a 'temporary property' is one like the property which belongs
to any particular man of walking in the gymnasium.
[The rendering of a property 'relatively' gives rise either to two
problems or to four. For if he at the same time render this property
of one thing and deny it of another, only two problems arise, as in
the case of a statement that it is a property of a man, in relation to
a horse, to be a biped. For one might try both to show that a man is
not a biped, and also that a horse is a biped: in both ways the
property would be upset. If on the other hand he render one apiece of
two attributes to each of two things, and deny it in each case of the
other, there will then be four problems; as in the case of a statement
that it is a property of a man in relation to a horse for the former
to be a biped and the latter a quadruped. For then it is possible to
try to show both that a man is not naturally a biped, and that he is a
quadruped, and also that the horse both is a biped, and is not a
quadruped. If you show any of these at all, the intended attribute is
demolished.]
An 'essential' property is one which is rendered of a thing in
comparison with everything else and distinguishes the said thing from
everything else, as does 'a mortal living being capable of receiving
knowledge' in the case of man. A 'relative' property is one which
separates its subject off not from everything else but only from a
particular definite thing, as does the property which virtue
possesses, in comparison with knowledge, viz. that the former is
naturally produced in more than one faculty, whereas the latter is
produced in that of reason alone, and in those who have a reasoning
faculty. A 'permanent' property is one which is true at every time,
and never fails, like being' compounded of soul and body', in the case