The paper tries to represent the polemic between the Stoics and the sceptically oriented Academy, concerning the abilities of human knowledge. It gives a brief account of the stoic epistemology on the basis of the characteristics of its criterion of knowledge – cataleptic fantasy. The description of the external and internal features of the latter is the ground of its criticism from Academy’s side. In its core this criticism tries to prove, that there is no fantasy meeting the strict claims of the Stoics criterion on the truth. The author shows the stoic response to the Academy criticism, which initiated the revision of the original stoic attitudes.