Note 5 — Chapter I

It may be noted that in this passage (Introduction, §§ 1 and 2) Kant is inconsistent in his use of the term 'pure'. Pure knowledge is introduced as a species of a priori knowledge: "A priori knowledge, if nothing empirical is mixed with it, is called pure". (B. 3, M. 2, 17.) And in accordance with this, the proposition 'every change has a cause' is said to be a priori but impure, because the conception of change can only be derived from experience. Yet immediately afterwards, pure, being opposed in general to empirical, can only mean a priori. Again, in the phrase 'pure a priori' (B. 4 fin., M. 3 med.), the context shows that 'pure' adds nothing to 'a priori', and the proposition 'every change must have a cause' is expressly given as an instance of pure a priori knowledge. The inconsistency of this treatment of the causal rule is explained by the fact that in the former passage he is thinking of the conception of change as empirical, while in the latter he is thinking of the judgement as not empirical. At bottom in this passage 'pure' simply means a priori.