The objection could then be raised as to what we are to make of a fool who cannot help but affirm that 2 + 2 = 22. How can we know that our inability to deny the cogito or mathematical truths is not a result of a weakness of our own? The answer to this question is not at all clear, and it is hard to give a better answer than that the fool who thinks that 2 + 2 = 22 ought to think harder before affirming his judgment.
We should also note that Descartes is a proponent of free will. The Meditator asserts that only the will, of all human mental faculties, is on an equal footing with God's, because it is unlimited. The will is free to affirm or deny whatever it wishes. In fact, free will is the source of error: if God had not blessed us with free will, we would not blithely pass judgments on our confused and obscure perceptions and we would never make mistakes.
The problem of free will and determinism is a common one in philosophy, and it is important that we explain the compatibilist position of Descartes. The problem runs something like this: "if we are a part of nature and subject to nature's deterministic laws, how is it that we can have free will?" Descartes' answer is that we do not have the "freedom of indifference," that we could have acted differently. All his conception of free will requires is that we have "freedom from external constraint," that we don't feel we are being forced into behaving as we do. We behave under the idea of freedom, and that is enough to ensure that our judgments are made freely.