A priori knowledge is propositional knowledge that can be had without experience. It is usually contrasted with a posteriori knowledge, which requires experience. Mathematics and logic are usually considered a priori disciplines. The natural and social sciences are usually considered a posteriori disciplines.
... January 20 - Dmitri Ivanovich Mendeleev, Russian chemist and inventor of the Periodic table
May 19 - Auguste Molinier, French historian
July 14 - Anton Chekhov, ...