One of C.G. Jung's fundamental contributions to the fields of psychology and epistemology is his concept of archetypes. For Jung, an archetype is a pattern of behavior. You can liken this concept to that of the structure of a crystal. While the crystalline structure predetermines the architecture of the actual crystal, until the crystal is given real form in matter, the pattern exists only as a concept. The archetype, then, is an abstract concept that has real lived meaning only when filled in with actual human experience. Like Kant's categories, an archetype is an a priori structure of cognition.