is brown, black, chair, table,
and every other nameable thing except fallible. Thus in Obversion and
Conversion by Contraposition, the homogeneity of the negative term is
tacitly assumed; it is assumed that A and not-A are of the same kind.

Now to apply this Law of our Thought to the interpretation of
propositions. Whenever a proposition is uttered we are entitled to
infer at once (or _immediately_) that the speaker has in his mind
some counter-proposition, in which what is overtly asserted of the
ostensible subject is covertly denied of another subject. And we must
know what this counter-proposition, the counter-implicate is, before
we can fully and clearly understand his meaning. But inasmuch as
any positive may have more than one contrapositive, we cannot tell
immediately or without some knowledge of the circumstances or context,
what the precise counter-implicate is. The peculiar fallacy incident
to this mode of interpretation is, knowing that there must be some
counter-implicate, to jump rashly or unwarily to the conclusion that
it is some definite one.

Dr. Bain applies the term Material Obverse to the form, Not-S is not
P, as distinguished from the form S is not not-P, which he calls
the Formal Obverse, on the ground that we can infer the
Predicate-contrapositive at once from the form, whereas we cannot tell
the Subject-contrapositive without an examination of the matter.
But in truth we cannot tell either Predicate-contrapositive or
Subject-contrapositive as it is in the mind of the speaker from
the bare utterance. We can only tell that if he has in his mind a
proposition definitely analysed into subject and predicate, he must
have contrapositives in his mind of both, and that they must be
homogeneous. Let a man say, "This book is a quarto". For all that we
know he may mean that it is not a folio or that it is not an
octavo: we only know for certain, under the law of Homogeneous
Counter-relativity, that he means some definite other size. Under
the same law, we know that he has a homogeneous contrapositive of the
subject, a subject that admits of the same predicate, some other book
in short. What the particular book is we do not know.

It would however be a waste of ingenuity to dwell upon the
manipulation of formulae founded on this law. The practical concern is
to know that for the interpretation of a proposition, a knowledge of
the counter-implicate, a knowledge of what it is meant to deny, is
essentia