The great diversity of our thoughts shows that we have Freewill.

For it is obviously clear from what I say that there are not Weights of Good and Evil conquering one another and being conquered by one another. For, behold, in a single hour one can think even a hundred good thoughts. And if because there was at that time much Good in a man, his good thoughts were numerous within, behold that man can do the reverse of this in the same hour. For directly after these good thoughts a man can think a multitude of evil thoughts. Which one of these, therefore, do they affirm to be more than the other ? And if they say that the Evil was most (in amount), how then since all that Evil would be in the man did it permit him to think all those good thoughts ? And if that Evil made room of its own Will, that Evil is good, which has this good Will. For how did that Evil which, when it wished, finally conquered the Good, consent to give way before it at first ? [Ov. p. 49.] But if they say that the Good exceeded (in amount), in which of a man's limbs, did all the Good hide itself, and make room for the small amount of Evil to go up and show a great victory ? If, therefore, the Evil submitted to give way before the Good, the Evil is better than the Good, in that it took the crown and gave it to its opponent. But if the Good consented to give place to the Evil that it (i.e., the Evil) might be victorious, the Good is more evil than the Evil in that it gave place to the Evil to do corruptly.