The exogenous approach to logic and its roots are discussed. The design of the exogenous propositional quantum logic (EQPL) is motivated by looking at states of quantum computers. A weakly complete proof system is given and the decidability of the logic is obtained as a corollary. An upper-bound to the complexity of both the SAT and model-checking problems of EQPL is derived. Finally, simplifications and dynamical extensions are discussed.