Stoic epistemology is usually assimilated to the Stoic theory of the criterion, namely ‘cognition’ (κατάληψις) and preconception (πρόληψις). Such assimilation is legitimate but needs to be further qualified. The Stoics considered science (ἐπιστήμη) to be accessible only to the Wise, defined virtue as a form of science and distinguished science from art (τέχνη), which has an identical structure: it consists in a coordinated system of ‘cognitions’ whose coherence and certainty is inferior to science, but accessible to non-wise persons. ‘Cognitive impression’ is the criterion coined by Zeno and it provoked polemics with the Academy: it is an impression in conformity with its object, whose existence was denied by the Academics. ‘Preconception’ was introduced by Chrysippus, who adapted Epicurean preconception, to which he gave a status beyond mere experience, though he denied ‘prenatal’ innatism.