That Logic is Necessary
When one of those who were present said, "Persuade me that logic is necessary," he replied: Do you wish me to prove this to you? The answer was, "Yes." Then I must use a demonstrative form of speech. This was granted. How then will you know if I am cheating you by argument? The man was silent. Do you see, said Epictetus, that you yourself are admitting that logic is necessary, if without it you cannot know so much as this, whether logic is necessary or not necessary