t' means that which receives treatment from a doctor, so
'object' means that which is known. And here we _can_ go on to make
the further parallel assertion that since knowledge is essentially the
knowledge of an object, an object is essentially an object of
knowledge. Just as 'patient' means a recipient of treatment, or, more
accurately, a sick man under treatment, so 'object' means something
known, or, more accurately, a reality known. And 'knowledge' and
'object of knowledge', like 'doctor' and 'patient', indicate the same
relation, though from different points of view, and, consequently,
when we can use the one term, we can use the other. But to say that an
object (i. e. a reality known) implies the knowledge of it is not to
say that reality implies the knowledge of it, any more than to say
that a patient implies a doctor is to say that a sick man implies a
doctor.

But a doctor, it might be objected, is not a fair parallel to
knowledge or a knower. A doctor, though an instance of a relative
term, is only an instance of one kind of relative term, that in which
the elements related are capable of existing apart from the relation,
the relation being one in which they can come to stand and cease to
stand. But there is another kind of relative term, in which the
elements related presuppose the relation, and any thought of these
elements involves the thought of the relation. A universal, e. g.
whiteness, is always the universal of certain individuals, viz.
individual whites; an individual, e. g. this white, is always an
individual of a universal, viz. whiteness. A genus is the genus of a
species, and vice versa. A surface is the surface of a volume, and a
volume implies a surface. A point is the end of a line, and a line is
bounded by points. In such cases the very being of the elements
related involves the relation, and, apart from the relation,
disappears. The difference between the two kinds of relative terms can
be seen from the fact that only in the case of the former kind can two
elements be found of which we can say significantly that their
relation is of the kind in question. We can say of two men that they
are related as doctor and patient, or as father and son, for we can
apprehend two beings as men without being aware of them as so related.
But of no two elements is it possible to say that their relation is
that of universal and individual, or of genus and species, or of
surface and volume; for to apprehend el