 His final answer is that both matter and form are principles of individuation: matter as the passive cause (causa receptiva; he also calls it the causa sine qua non), form as the active cause (QLIIS 17, 64). Individuation is achieved when the last species (the species specialissima) completes the individual (QLIIS 17, 67). Form, arriving at matter, designates matter and designating matter, designates itself. The designative action (signatio) of form on matter is the cause of an actual existing being (QLIS 71).