61. The Stoic School. -- The Stoics unanimously inculcated the supreme importance of Ethics. Some of them even went so far as to forbid all other study. That, however, was not the attitude of the leading representatives of stoicism. ZENO OF CITIUM (about 342-270), the founder of the school, CLEANTHUS, his immediate successor (about 331-251), CHRYSIPPUS (about 281-208), the popular exponent and systematizer of the Stoic doctrines, -- all three expressly recommend the study of Physics in its relation to morals. They also recognized the necessity of Logic among the philosophical sciences; for it teaches us how to discern truth from falsehood, and it is all-important that our conduct be based upon certain knowledge.^{1} We shall outline the principal doctrines of the Stoics on physics and ethics.

{1} The Stoics took up a large number of the problems of formal logic treated by Aristotle, notably those on the categories and the syllogism. Without having much intrinsic value, their system of logic is none the less original. It is entirely conceptualist.