In his treatment of logic, Zeno was influenced by Stilpo and the other Megarians. Zeno urged the need to lay down a basis for logic because the wise person must know how to avoid deception. Cicero accused Zeno of being inferior to his philosophical predecessors in his treatment of logic, and it seems true that a more exact treatment of the subject was laid down by his successors, including Chrysippus. Zeno divided true conceptions into the comprehensible and the incomprehensible, permitting for free-will the power of assent ("sinkatathesis"/συνκατάθεσις) in distinguishing between sense impressions. Zeno said that there were four stages in the process leading to true knowledge, which he illustrated with the example of the flat, extended hand, and the gradual closing of the fist: