Jung’s personality theory, originally a guide for psychoanalysts seeking patterns in clients’ psyches, has until now been entirely qualitative and free of numbers. Its quantification to come must be based on and be consistent with this qualitative description. This chapter places this informal set of descriptions on an axiomatic foundation so that typological “principles” can be deduced logically and rigorously as in Euclid’s classical geometry. To make this accessible to the non-mathematical reader, the presentation will be kept informal rather than being expressed in the dry theorems and corollaries of high school.