If I say that 50% of birds are black, and so I then say that I have a 50% chance of choosing a black bird if I pick a bird at random, is this an a priori or a posteriori proposition? Since given the premise it's true, but the premise itself requires empirical evidence.
"A priori” and “a posteriori” refer primarily to how, or on what basis, a proposition might be known. In general terms, a proposition is knowable a priori if it is knowable independently of experience, while a proposition knowable a posteriori is knowable on the basis of experience. The distinction between a priori and a posteriori knowledge thus broadly corresponds to the distinction between empirical and nonempirical knowledge.
Thus, "a proposition that require empirical evidence" is not a priori.