Analyticity, the a priori and necessity
What does Kant say ? That if a judgment is analytic, its denial will
involve a contradiction because the predicate is contained in the subject :
That a body is extended is a proposition that holds a priori and is not
empirical. For, before appealing to experience, I have already in the
concept of body all the conditions required for my judgment. I have
only to extract from it, in accordance with the principle of contradiction,
the required predicate, and in so doing can at the same time become
conscious of the necessity of the judgment - and that is what experience
could never have taught me (B 11-2).
The clearest expression is perhaps the following:
For, if the judgment is analytic, whether affirmative or negative, its truth can
always be known in accordance with the principle of contradiction (B. 190,
italics in original).
The principle of contradiction must therefore be recognised as being the
universal and completely sufficient principle of all analytic knowledge; but
beyond the sphere of analytic knowledge it has, as a sufficient criterion
of truth, no authority and no field of application (B. 191).
These quotations need to be taken in conjunction with Kant's
definition of the principle of contradiction: 'The proposition that no
predicate contradictory of a thing can belong to it, is entitled the principle of contradiction, and is a universal, though merely negative,
criterion of all truth' (B. 190). To take his own earlier example, to say
'This body is not extended' is contradictory because we are both affirming
and denying extension of it. But we know we are doing this because the
predicate 'extended' is contained in the subject 'body' as part of its
definition; it is because 'All bodies are extended' is an analytic truth that
the principle of contradiction manages to get a grasp on the situation.
In ordinary cases we have to extract a contradiction by putting together
an earlier statement of the speaker with a later one: 'Yesterday you said
that it was square, but today you refer to its three sides'. In such cases
one of the contradictory statements must be given up, though it is open
to us which one to surrender. In the case of analytic judgments we have
no option; by using that particular word as the subject we are com-
mitted to the definition and this is why a 'merely negative' criterion of
truth is applicable. (Anthony Manser, 'How Did Kant Define 'Analytic'?', Analysis, Vol. 28, No. 6 (Jun., 1968), pp. 197-199 : 198.)
The (or a) 'use' of analytic propositions appears to be then that in empirical matters they reveal a necessity which 'experience could never have taught me'. Kant does not deny that I need experience (e.g. of bodies and the meanings of words) in order to formulate an analytic judgement or proposition. When Kant says, 'before appealing to experience, I already have in the concept of body all the conditions required for my judgment', he does not mean 'before having had any experience'; he means 'merely using what experience I have' and without having to make further, extra or special investigative appeal to experience.