Kant a priori and a posteriori

In Proglegomena, Kant discusses the distinction between a priori and a posteriori knowledge, being that a priori means that we know something independently of observation and a posteriori means that we know something through observation. These two forms of knowledge are the only ways in which humans can experience the world and learn things. His thinking of a priori knowledge is usually based upon mathematical truths that cannot be done in any other way.