Critique_.

Further, the distinction drawn between _a priori_ judgements in
mathematics and in physics is largely responsible for the difficulty
of understanding what Kant means by _a priori_. His unfortunate
tendency to explain the term negatively could be remedied if it could
be held either that the term refers solely to mathematical judgements
or that he considers the truth of the law of causality to be
apprehended in the same way that we see that two and two are four. For
an _a priori_ judgement could then be defined as one in which the
mind, on the presentation of an individual in perception or
imagination, and in virtue of its capacity of thinking, apprehends the
necessity of a specific relation. But this definition is precluded by
Kant's view that the law of causality and similar principles, though
_a priori_, are not self-evident.

CHAPTER II

THE SENSIBILITY AND THE UNDERSTANDING

The distinction between the sensibility and the understanding[1] is
to Kant fundamental both in itself and in relation to the conclusions
which he reaches. An outline, therefore, of this distinction must
precede any statement or examination of the details of his position.
Unfortunately, in spite of its fundamental character, Kant never
thinks of questioning or criticizing the distinction in the form in
which he draws it, and the presence of certain confusions often
renders it difficult to be sure of his meaning.

[1] Cf. B. 1, 29, 33, 74-5, 75, 92-4; M. 1, 18, 21, 45-46,
57.

The distinction may be stated in his own words thus: "There are two
stems of human knowledge, which perhaps spring from a common but to us
unknown root, namely sensibility and understanding."[2] "Our knowledge
springs from two fundamental sources of the mind; the first receives
representations[3] (receptivity for impressions); the second is the
power of knowing an object by means of these representations
(spontaneity of conceptions). Through the first an object is _given_
to us; through the second the object is _thought_ in relation to the
representation (which is a mere determination of the mind). Perception
and conceptions constitute, therefore, the elements of all our
knowledge, so that neither conceptions without a perception in some
way corresponding to them, nor perception without conceptions can
yield any knowledge.... Neither of these qualities has a preference
over the other. Without sensibility no object would be given to us,
an