and Definition.

Sec. 7. Contradictory Relative Terms.--Every term has, or may have, another
corresponding with it in such a way that, whatever differential
qualities (Sec. 5) it connotes, this other connotes merely their absence;
so that one or the other is always formally predicable of any Subject,
but both these terms are never predicable of the same Subject in the
same relation: such pairs of terms are called Contradictories. Whatever
Subject we take, it is either visible or invisible, but not both; either
human or non-human, but not both.

This at least is true formally, though in practice we should think
ourselves trifled with if any one told us that 'A mountain is either
human or non-human, but not both.' It is symbolic terms, such as X and
x, that are properly said to be contradictories in relation to any
subject whatever, S or M. For, as we have seen, the ordinary use of
terms is limited by some _suppositio_, and this is true of
Contradictories. 'Human' and 'non-human' may refer to zoological
classification, or to the scope of physical, mental, or moral powers--as
if we ask whether to flourish a dumbbell of a ton weight, or to know the
future by intuition, or impeccability, be human or non-human. Similarly,
'visible' and 'invisible' refer either to the power of emitting or
reflecting light, so that the words have no hold upon a sound or a
scent, or else to power of vision and such qualifications as 'with the
naked eye' or 'with a microscope.'

Again, the above definition of Contradictories tells us that they cannot
be predicated of the same Subject "in the same relation"; that is, at
the same time or place, or under the same conditions. The lamp is
visible to me now, but will be invisible if I turn it out; one side of
it is now visible, but the other is not: therefore without this
restriction, "in the same relation," few or no terms would be
contradictory.

If a man is called wise, it may mean 'on the whole' or 'in a certain
action'; and clearly a man may for once be wise (or act wisely) who, on
the whole, is not-wise. So that here again, by this ambiguity, terms
that seem contradictory are predicable of the same subject, but not "in
the same relation." In order to avoid the ambiguity, however, we have
only to construct the term so as to express the relation, as 'wise on
the whole'; and this immediately generates the contradictory 'not-wise
on the whole.' Similarly, at one age a man may have black hair, at