Discourses 2.25

When someone in his audience said, Convince me that logic is necessary, he answered: Do you wish me to demonstrate this to you?—Yes.—Well, then, must I use a demonstrative argument?—And when the questioner had agreed to that, Epictetus asked him. How, then, will you know if I impose upon you?—As the man had no answer to give, Epictetus said: Do you see how you yourself admit that all this instruction is necessary, if, without it, you cannot so much as know whether it is necessary or not?

Epictetus, Discourses 2.25, translated by W. A. Oldfather

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 my 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?

Epictetus, Discourses 2.25, translated by George Long

When one of his audience said, 'Convince me that logic is useful,' he said,

Would you have me demonstrate it?

'Yes.'

Well, then, must I not use a demonstrative argument?

And, when the other agreed, he said, How then shall you know if I impose upon you? And when the man had no answer, he said, You see how you yourself admit that logic is necessary, if without it you are not even able to learn this much—whether it is necessary or not.

Epictetus, Discourses 2.25, translated by P. E. Matheson