The fourth influence: After he had left the Manichaean group, he fell intoskepticism, as always happens if you are disappointed about a system of truth in which you believe, suppressing other elements of truth which are in you but which you do not admit; then if you cannot keep them down any more., you fall into a skeptical doubt about every possibility of truth.

In his period skepticism was a very widely spread mood. Even in the later Academy, i, e., the Platonic school, skepticism about knowledge was present in terms of what is called probabilism: only probable statements are possible; no certainty is possible.