who have not properly exercised their perceptions fall into irregularity and thoughtlessness. Again, without dialectics, the wise man cannot be acute, and ingenious, and wary, and altogether dangerous as an arguer. For that it belongs to the same man to speak correctly and to reason correctly, and to discuss properly those subjects which are proposed to him, and to answer readily whatever questions are put to him, all which qualities belong to a man who is skilful in dialectics. This then is a brief summary of their opinions on logic.
XXXVI. And, that we may also enter into some more minute details respecting them, we will subjoin what refers to what they call their introductory science, as it is stated by Diocles, of Magnesia, in his Excursion of Philosophers, where he speaks as follows, and we will give his account word for word.
The Stoics have chosen to treat, in the first place, of perception and sensation, because the criterion by which the truth of