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. [1] Locke's _Essay_, i, 1, §§ 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.