Empiricism is the philosophical view that most, or all, knowledge is derived from experience. This means both senses and inner thought—contrary to rationalism.
Empiricism holds that knowledge, because it is based soley on the past, can never reach a level of absolute certainty—only high probability.
Few empiricists deny the possibility of a priori knowledge, that is, things that are known intuitively through reason rather than direct experience. The laws of logic and mathematics are examples of a priori knowledge. (John Stuart Mill, though, still held that we come to learn how to acquire this knwoledge through experience.)
Despite this acceptance of some rational knowledge, empiricists reject the idea that reason produces any certain knowledge about the world itself. Empiricists also strongly deny the existence of any innate knowledge, that is, any knowledge that exists in the mind prior to experience or rational activity (ideas that one is supposedly born with, for example).