The Complete Aristotle (eng.)

qualification good good for each, so it is our task to
start from what is more knowable to oneself and make what is
knowable by nature knowable to oneself. Now what is knowable and
primary for particular sets of people is often knowable to a very
small extent, and has little or nothing of reality. But yet one
must start from that which is barely knowable but knowable to
oneself, and try to know what is knowable without qualification,
passing, as has been said, by way of those very things which one
does know.
<
    div id="section79" class="section" title="4">
4
    Since at the start we distinguished the various marks by which
we determine substance, and one of these was thought to be the
essence, we must investigate this. And first let us make some
linguistic remarks about it. The essence of each thing is what it
is said to be propter se. For being you is not being musical, since
you are not by your very nature musical. What, then, you are by
your very nature is your essence.
    Nor yet is the whole of this the essence of a thing; not that
which is propter se as white is to a surface, because being a
surface is not identical with being white. But again the
combination of both-’being a white surface’-is not the essence of
surface, because ‘surface’ itself is added. The formula, therefore,
in which the term itself is not present but its meaning is
expressed, this is the formula of the essence of each thing.
Therefore if to be a white surface is to be a smooth surface, to be
white and to be smooth are one and the same.
    But since there are also compounds answering to the other
categories (for there is a substratum for each category, e.g. for
quality, quantity, time, place, and motion), we must inquire
whether there is a formula of the essence of each of them, i.e.
whether to these compounds also there belongs an essence, e.g.
‘white man’. Let the compound be denoted by ‘cloak’. What is the
essence of cloak? But, it may be said, this also is not a propter
se expression. We reply that there are just two ways in which a
predicate may fail to be true of a subject propter se, and one of
these results from the addition, and the other from the omission,
of a determinant. One kind of predicate is not propter se because
the term that is being defined is combined with another
determinant, e.g. if in defining the essence of white one were to
state the formula of white man; the other because in the subject
another determinant is combined with that which is expressed in the
formula, e.g. if ‘cloak’ meant ‘white man’, and one were to define
cloak as white; white man is white indeed, but its essence is not
to be white.
    But is being-a-cloak an essence at all? Probably not. For the
essence is precisely what something is; but when an attribute is
asserted of a subject other than itself, the complex is not
precisely what some ‘this’ is, e.g. white man is not precisely what
some ‘this’ is, since thisness belongs only to substances.
Therefore there is an essence only of those things whose formula is
a definition. But we have a definition not where we have a word and
a formula identical in meaning (for in that case all formulae or
sets of words would be definitions; for there will be some name for
any set of words whatever, so that even the Iliad will be a
definition), but where there is a formula of something primary; and
primary things are those which do not imply the predication of one
element in them of another element. Nothing, then, which is not a
species of a genus will have an essence-only species will have it,
for these are thought to imply not merely that the subject
participates in the attribute and has it as an affection, or has it
by accident; but for ever thing else as well, if it has a name,
there be a formula of its meaning-viz. that this attribute belongs
to this subject; or instead of a simple formula we shall be able to
give a more accurate one; but there will be no definition nor
essence.
    Or has ‘definition’, like ‘what a thing is’, several meanings?
‘What a thing is’ in one sense means substance and the ‘this’, in
another one or other of the predicates, quantity, quality, and the
like. For as ‘is’ belongs to all things, not however in the same
sense, but to one sort of thing primarily and to others in a
secondary way, so too ‘what a thing is’ belongs in the simple sense
to substance, but in a limited sense to the other categories. For
even of a quality we might ask what