The Complete Aristotle (eng.)

nothing, while any that
belongs to all the things that fall under the same genus does not
separate it off from the things contained in the same genus. Any
addition, then, of that kind will be pointless.
    Or see if, though the additional matter may be peculiar to the
given term, yet even when it is struck out the rest of the
expression too is peculiar and makes clear the essence of the term.
Thus, in the definition of man, the addition ‘capable of receiving
knowledge’ is superfluous; for strike it out, and still the
expression is peculiar and makes clear his essence. Speaking
generally, everything is superfluous upon whose removal the
remainder still makes the term that is being defined clear. Such,
for instance, would also be the definition of the soul, assuming it
to be stated as a ‘self-moving number’; for the soul is just ‘the
self-moving’, as Plato defined it. Or perhaps the expression used,
though appropriate, yet does not declare the essence, if the word
‘number’ be eliminated. Which of the two is the real state of the
case it is difficult to determine clearly: the right way to treat
the matter in all cases is to be guided by convenience. Thus (e.g.)
it is said that the definition of phlegm is the ‘undigested
moisture that comes first off food’. Here the addition of the word
‘undigested’ is superfluous, seeing that ‘the first’ is one and not
many, so that even when undigested’ is left out the definition will
still be peculiar to the subject: for it is impossible that both
phlegm and also something else should both be the first to arise
from the food. Or perhaps the phlegm is not absolutely the first
thing to come off the food, but only the first of the undigested
matters, so that the addition ‘undigested’ is required; for stated
the other way the definition would not be true unless the phlegm
comes first of all.
    Moreover, see if anything contained in the definition fails to
apply to everything that falls under the same species: for this
sort of definition is worse than those which include an attribute
belonging to all things universally. For in that case, if the
remainder of the expression be peculiar, the whole too will be
peculiar: for absolutely always, if to something peculiar anything
whatever that is true be added, the whole too becomes peculiar.
Whereas if any part of the expression do not apply to everything
that falls under the same species, it is impossible that the
expression as a whole should be peculiar: for it will not be
predicated convertibly with the object; e.g. ‘a walking biped
animal six feet high’: for an expression of that kind is not
predicated convertibly with the term, because the attribute ‘six
feet high’ does not belong to everything that falls under the same
species.
    Again, see if he has said the same thing more than once, saying
(e.g.) ‘desire’ is a ‘conation for the pleasant’. For ‘desire’ is
always ‘for the pleasant’, so that what is the same as desire will
also be ‘for the pleasant’. Accordingly our definition of desire
becomes ‘conation-for-the-pleasant’: for the word ‘desire’ is the
exact equivalent of the words ‘conation for-the-pleasant’, so that
both alike will be ‘for the pleasant’. Or perhaps there is no
absurdity in this; for consider this instance:-Man is a biped’:
therefore, what is the same as man is a biped: but ‘a walking biped
animal’ is the same as man, and therefore walking biped animal is a
biped’. But this involves no real absurdity. For ‘biped’ is not a
predicate of ‘walking animal’: if it were, then we should certainly
have ‘biped’ predicated twice of the same thing; but as a matter of
fact the subject said to be a biped is’a walking biped animal’, so
that the word ‘biped’ is only used as a predicate once. Likewise
also in the case of ‘desire’ as well: for it is not ‘conation’ that
is said to be ‘for the pleasant’, but rather the whole idea, so
that there too the predication is only made once. Absurdity
results, not when the same word is uttered twice, but when the same
thing is more than once predicated of a subject; e.g. if he says,
like Xenocrates, that wisdom defines and contemplates reality:’ for
definition is a certain type of contemplation, so that by adding
the words ‘and contemplates’ over again he says the same thing
twice over. Likewise, too, those fail who say that ‘cooling’ is
‘the privation of natural heat’. For