put
up with the illusory knowledge offered by contemporary philosophy. Now
the objects of metaphysics, God, freedom, and immortality, are not
objects of experience in the sense in which a tree or a stone is an
object of experience. Hence our views about them cannot be due to
experience; they must somehow be apprehended by pure reason, i. e. by
thinking and without appeal to experience. Moreover, it is in fact by
thinking that men have always tried to solve the problems concerning
God, freedom, and immortality. What, then, is the cause of the
unsatisfactory treatment of these problems and men's consequent
indifference? It must, in some way, lie in a failure to attain the
sure scientific method, and really consists in the neglect of an
inquiry which should be a preliminary to all others in metaphysics.
Men ought to have begun with a critical investigation of pure reason
itself. Reason should have examined its own nature, to ascertain in
general the extent to which it is capable of attaining knowledge
without the aid of experience. This examination will decide whether
reason is able to deal with the problems of God, freedom, and
immortality at all; and without it no discussion of these problems
will have a solid foundation. It is this preliminary investigation
which the _Critique of Pure Reason_ proposes to undertake. Its aim is
to answer the question, 'How far can reason go, without the material
presented and the aid furnished by experience?' and the result
furnishes the solution, or at least the key to the solution, of all
metaphysical problems.

Kant's problem, then, is similar to Locke's. Locke states[1] that his
purpose is to inquire into the original, certainty, and extent of
human knowledge; and he says, "If, by this inquiry into the nature of
the understanding I can discover the powers thereof; how far they
reach, to what things they are in any degree proportionate, and where
they fail us; I suppose it may be of use to prevail with the busy mind
of man, to be more cautious in meddling with things exceeding its
comprehension; to stop when it is at the utmost extent of its tether;
and to sit down in a quiet ignorance of those things, which, upon
examination, are found to be beyond the reach of our capacities."
Thus, to use Dr. Caird's analogy,[2] the task which both Locke and
Kant set themselves resembled that of investigating a telescope,
before turning it upon the stars, to determine its competence for the
work.