[1] Locke's _Essay_, i, 1, Secs. 2, 4.

[2] Caird, i, 10.

The above outline of Kant's problem is of course only an outline. Its
definite formulation is expressed in the well-known question, 'How are
_a priori_ synthetic judgements possible?'[3] To determine the meaning
of this question it is necessary to begin with some consideration of
the terms '_a priori_' and 'synthetic'.

[3] B. 19, M. 12.

While there is no difficulty in determining what Kant would have
recognized as an _a priori_ judgement, there is difficulty in
determining what he meant by calling such a judgement _a priori_. The
general account is given in the first two sections of the
Introduction. An _a priori_ judgement is introduced as something
opposed to an _a posteriori_ judgement, or a judgement which has its
source in experience. Instances of the latter would be 'This body is
heavy', and 'This body is hot'. The point of the word 'experience' is
that there is direct apprehension of some individual, e. g. an
individual body. To say that a judgement has its source in experience
is of course to imply a distinction between the judgement and
experience, and the word 'source' may be taken to mean that the
judgement depends for its validity upon the experience of the
individual thing to which the judgement relates. An _a priori_
judgement, then, as first described, is simply a judgement which is
not _a posteriori_. It is independent of all experience; in other
words, its validity does not depend on the experience of individual
things. It might be illustrated by the judgement that all three-sided
figures must have three angles. So far, then, no positive meaning has
been given to _a priori_.[4]

[4] Kant is careful to exclude from the class of _a priori_
judgements proper what may be called relatively _a priori_
judgements, viz. judgements which, though not independent of
all experience, are independent of experience of the facts to
which they relate. "Thus one would say of a man who
undermined the foundations of his house that he might have
known _a priori_ that it would fall down, i. e. that he did
not need to wait for the experience of its actual falling
down. But still he could not know this wholly _a priori_, for
he had first to learn through experience that bodies are
heavy and consequently fall, if their supports are taken
away." (B. 2, M. 2.)

Kant then proceeds, not as we should