This is an excerpt from Critique of Pure Reason, B13:
Take the proposition: "Everything that happens has its cause." In the concept of something that happens, I think, to be sure, of an existence that was preceded by a time, etc., and from that analytic judgments can be drawn. But the concept of a cause lies entirely outside that concept, anda indicates something different than the concept of what happens in general, and is therefore not contained in the latter representation at all. How then do I come to say something quite different about that which happens in general, and to cognize the concept of cause as belonging to it, indeed necessarily,' even though not contained in it?d What is the unknown =X here on which the understanding depends when it believes itself to discover beyond the concept of A a predicate that is foreign to it yet which it nevertheless believes to be connected with it?fIt cannot be experience, for the principle that has been adduced adds the latter representations to the former not only with greater generality than experience can provide, but also with the expression of necessity, hence entirely a priori and from mere concepts. Now the entire final aim of our speculative a priori cognition rests on such synthetic, i.e., ampliative principles; for the analytic ones are, to be sure, most important and necessary, but only for attaining that distinctness of con. cepts which is requisite for a secure and extended synthesis as a really new acquisition.
Does Kant mean that "Everything that happens has its cause" is synthetic a priori, but "Something that happens has a cause" is analytic a priori?