e meaning, the fact
asserted or denied, is what we are really concerned to prove or
disprove; that a mere change in the words that constitute our terms, or
of construction, does not affect the truth of a proposition as long as
the meaning is not altered, or (rather) as long as no fresh meaning is
introduced; and that if the meaning of any proposition is true, any
other proposition that denies it is false. This postulate is plainly
necessary to consistency of statement and discourse; and consistency is
necessary, if our thought or speech is to correspond with the unity and
coherence of Nature and experience; and the Laws of Thought or
Conditions of Immediate Inference are an analysis of this postulate.

Sec. 4. The principle of Identity is usually written symbolically thus: _A
is A; not-A is not-A_. It assumes that there is something that may be
represented by a term; and it requires that, in any discussion, _every
relevant term, once used in a definite sense, shall keep that meaning
throughout_. Socrates in his father's workshop, at the battle of Delium,
and in prison, is assumed to be the same man denotable by the same name;
and similarly, 'elephant,' or 'justice,' or 'fairy,' in the same
context, is to be understood of the same thing under the same
_suppositio_.

But, further, it is assumed that of a given term another term may be
predicated again and again in the same sense under the same conditions;
that is, we may speak of the identity of meaning in a proposition as
well as in a term. To symbolise this we ought to alter the usual
formula for Identity and write it thus: _If B is A, B is A; if B is
not-A, B is not-A_. If Socrates is wise, he is wise; if fairies frequent
the moonlight, they do; if Justice is not of this world, it is not.
_Whatever affirmation or denial we make concerning any subject, we are
bound to adhere to it for the purposes of the current argument or
investigation._ Of course, if our assertion turns out to be false, we
must not adhere to it; but then we must repudiate all that we formerly
deduced from it.

Again, _whatever is true or false in one form of words is true or false
in any other_: this is undeniable, for the important thing is identity
of meaning; but in Formal Logic it is not very convenient. If Socrates
is wise, is it an identity to say 'Therefore the master of Plato is
wise'; or, further that he 'takes enlightened views of life'? If _Every
man is fallible_, is it an identical pro