Will, Thinking, Proof

Insofar as Will is a species of Thinking, as it is in the Meditations, it is bound by the laws of the Intellect.  So, for example, on the basis of that classification, it is logically impossible to doubt the existence of God once that is proven in the Third Meditation.  In contrast, insofar as Will is independent of Thinking, as it is in the Rules for the Direction of the Mind, its operations, e. g. Doubting, Disbelief, Denial, etc. are not bound by the Law of Contradiction.  So, for example, on that basis the result of the Third Meditation does not entail the indubitability of the existence of God.  Thus, though Descartes never explains the subsumption of Will under Thinking in the later work, it does eliminate from its development a profound complication.