Critique of Pure Reason.
"In the applications of the pure conceptions of the understanding to possible experience, the use of their synthesis is either mathematical or dynamical; for it is directed partly merely to the intuition, and partly to the existence of a phenomenon in general. But the conditions a priori of the intuitions are, in respect to a possible experience, absolutely necessarily; those of the existence of the objects of a possible empirical intuition are only in themselves contingent. Hence the principles of mathematical use are ... absolutely necessary; that is, they strike apodictically; whilst those of dynamic use will also carry with them the character of a necessity a priori, but only under the condition of the empirical thinking in an experience...."
I'm not sure I grasp this fully. The premise behind it is the old distinction between contingent and necessary truths. It is a contingent truth that Smith owns a Hewlett-Packard laptop. It is a necessary truth that the owner of a Hewlett-Packard laptop owns at least one laptop.
But Kant is making another distinction within the "necessary" component of that distinction. There are mathematical necessities and dynamical necessities. I'm not clear why this distinction is important to him.
2+2 is four is a mathematical necessity.
The above example, though, the proposition that the "owner of a Hewlett-Packard laptop owns at least one laptop" may qualify as a dynamic necessity. There is a "condition of the empirical thinking" at work here, t hat is, that the world contains laptops of different brands, that H-P is one of them, etc, Our statement "carries with it" necessity, but only after such empirical facts are understood.
At least I think that's what he's saying. Readers should feel free to correct me.