"Would you have me demonstrate it to you?" says he.
"Then I must use a demonstrative form of argument."
"And how will you know then whether I argue sophistically?"
On this, the man being silent, "You see," says he, "that even by your own confession, logic is necessary; since without its assistance, you cannot learn so much as whether it be necessary or not."
EPICTETUS. DISCOURSES. Book ii. §25. ¶1.