The diversity among men proves that Freewill exists.

And if there is no Freewill, does not this Controversy in which we are involved concerning Freewill, bear witness that we have Freewill ? For a 'bound Nature' could not utter all these various matters controversially. For if all mankind were alike saying one thing or doing one thing, perhaps there would be an opportunity to make the mistake (of thinking) that there is no Freewill. But if even the Freewill of a single man undergoes many variations in a single day so that he is good or evil, hateful or pleasing, merciful or merciless, bitter or pleasant, blessing or cursing, grateful or ungrateful, [Ov. p. 46.] so that he resembles both God and Satan, is it not established by thousands of witnesses that we have Freewill ? And, behold, at the mouth of two or three witnesses is every word established. [Deut. xix 15. S. Matt. xviii. 16.]