Omnipotence and the good
On the axis: The source of morality · God's will
If God is all-powerful, does the good depend on his will to the point that he could have commanded otherwise? Descartes ventures it for the eternal truths, Ockham for certain precepts of the moral law, and arbitrariness looms.
Justification
The cogito at first secures only my own existence: so long as an evil genius could deceive me even in my self-evident truths, doubt is not defeated. Proving God therefore becomes the keystone of the system. Descartes offers two proofs: the idea of infinity within me, which cannot arise from a finite being, demands an infinite cause (Meditation III); and existence belongs to the essence of the perfect being as the equality of its angles belongs to the triangle, the ontological proof (Meditation V). Now a perfect God cannot be a deceiver, deception betraying a defect: his veracity therefore guarantees that what I conceive clearly and distinctly is true. Far from inherited theism, the position is the keystone that lifts doubt and grounds the whole of science.
Meditations on First Philosophy, III and V · Discourse on Method, IV
Anchors: Descartes · Ockham
leads to: Existence of God