"thought is free" Sir Andrew is trying to match wits with Maria, and he doesn't have a chance. He asked her if she thought that she "had fools in hand," meaning, "Do you think you're dealing with fools?" She replied "Sir, I have not you by th' hand," meaning that if she had him by the hand, she would be sure that she had a fool in hand. But he thinks—who can guess how a fool thinks?—that somehow he will prove that he is not a fool by giving her his hand. Her "thought is free" means, "no matter what you do I can still think what I think, which is that you are still a fool, no matter what you do."