| These contradictions place the work in an unfavourable light in the eyes of those who rely on the judgement of others, but are easily reconciled by those who have mastered the idea of the whole. |
| If a theory possesses stability in itself, the action and reaction which seemed at first to threaten its existence serve only, in the course of time, to smooth down any superficial roughness or inequality, and--if men of insight, impartiality, and truly popular gifts, turn their attention to it--to secure to it, in a short time, the requisite elegance also. |
| Konigsberg, April 1787. INTRODUCTION |
| I. Of the difference between Pure and Empirical Knowledge |
| That all our knowledge begins with experience there can be no doubt. |
| For how is it possible that the faculty of cognition should be awakened into exercise otherwise than by means of objects which affect our senses, and partly of themselves produce representations, partly rouse our powers of understanding into activity, to compare to connect, or to separate these, and so to convert the raw material of our sensuous impressions into a knowledge of objects, which is called experience? |
| In respect of time, therefore, no knowledge of ours is antecedent to experience, but begins with it. |
| But, though all our knowledge begins with experience, it by no means follows that all arises out of experience. |
| For, on the contrary, it is quite possible that our empirical knowledge is a compound of that which we receive through impressions, and that which the faculty of cognition supplies from itself (sensuous impressions giving merely the occasion), an addition which we cannot distinguish from the original element given by sense, till long practice has made us attentive to, and skilful in separating it. |
| It is, therefore, a question which requires close investigation, and not to be answered at first sight, whether there exists a knowledge altogether independent of experience, and even of all sensuous impressions? |
| Knowledge of this kind is called a priori, in contradistinction to empirical knowledge, which has its sources a posteriori, that is, in experience. |
| But the expression, "a priori," is not as yet definite enough adequately to indicate the whole meaning of the question above started. |
| For, in speaking of knowledge which has its sources in experience, we are wont to say, that this or that may be known a priori, because we do not derive this knowledge immediately from experience, but from a general rule, which, however, we have itself borrowed from experience. |
| Thus, if a man undermined his house, we say, "he might know a priori that it would have fallen;" that is, he needed not to have waited for the experience that it did actually fall. |
| But still, a priori, he could not know even this much. |
| For, that bodies are heavy, and, consequently, that they fall when their supports are taken away, must have been known to him previously, by means of experience. |
| By the term "knowledge a priori," therefore, we shall in the sequel understand, not such as is independent of this or that kind of experience, but such as is absolutely so of all experience. |
| Opposed to this is empirical knowledge, or that which is possible only a posteriori, that is, through experience. |
| Knowledge a priori is either pure or impure. |
| Pure knowledge a priori is that with which no empirical element is mixed up. |
| For example, the proposition, "Every change has a cause," is a proposition a priori, but impure, because change is a conception which can only be derived from experience. |