Descartes' Philosophical Arguments for God's Existence

René Descartes' philosophical system begins with the indubitable truth of the cogito: "I think, therefore I am." From this foundational certainty of our own existence and thought, Descartes proceeds to demonstrate the existence of God. He asserts that without proving God's existence and goodness, it is impossible to achieve certainty about anything else, as a deceptive God could undermine all our perceptions.

The Argument from Innate Ideas and Perfection

Descartes posits that all that exists in our mind for conceiving things are ideas. Among the various types of ideas, some are neither derived from external things nor created by our imagination; these are innate ideas. They arise from the mere capacity to think, by the lumen naturale rationis (natural light of reason), and are so self-evident that we judge them to be true (much like the thought or existence of the cogito ergo sum).

One such innate idea is that of perfection. Since I, as a thinking being, doubt, I am inherently imperfect. Therefore, the idea of perfection cannot originate from me, an imperfect being. It must, consequently, have its origin in a perfect being that has placed this idea within me. This perfect being, God, must exist, as existence itself is one of the possible perfections. Furthermore, a perfect being cannot deceive, as deception is a flaw. From this, Descartes concludes that God, the perfect being, is truthful.

Since God does not deceive, and through the principle of efficient causality, we can trust that things causing our adventitious ideas (ideas derived from sensory experience) truly exist.

Additional Proofs for God's Existence

Descartes provides two further arguments to demonstrate God's existence:

1. Proof from Self-Existence and Preservation

   Although the self exists, it is not self-caused, for that would imply it is perfect, which it is not. Therefore, the existence of God, a perfect being, is necessary to have created and to preserve me. I depend on God for my being and continued existence. This is because an imperfect, finite thinking substance (like myself) cannot be the cause of itself, nor can it contain the idea of an infinite thinking substance. To admit otherwise would mean that the imperfect is the cause of something more perfect, which is a logical error.

   Moreover, even if a finite thinking substance were created by another finite thinking substance that possessed the idea of an infinite thinking substance, this idea would ultimately have to originate from a prior substance. Since the chain of finite thinking substances cannot be infinite, there must ultimately be an infinite thinking substance that is the original cause of the idea of infinity in all finite thinking substances.

   While we may believe we are begotten by parents, they give us birth but are not the cause of our being as a thinking thing, nor of our continuous preservation in being. We might also imagine that many things contributed to our production, each imparting an idea of the perfections we attribute to God. However, this does not negate the need for a single, ultimate perfect source.

2. The Cartesian Ontological Argument

   This is Descartes' most widely discussed argument. Consider a triangle: it clearly has three sides, and this is true, but it does not necessitate the triangle's actual existence. Similarly, one might argue that while God is conceived as a being whose essence includes existence, this could merely be an invention of the mind, implying no necessity for God's actual existence.

   Descartes resolves this by pointing out a hidden fallacy in such reasoning. Just as one cannot conceive of a mountain without a valley (though neither the mountain nor the valley necessarily exists), the two concepts are inseparable. Whether they exist or not, the mountain and the valley are always conceived together. Similarly, Descartes argues, I cannot conceive of God without conceiving of God's existence. The idea of God and the idea of existence are inseparable in the concept of God. Therefore, when I inevitably conceive of God, I must conceive of God as existing.

God's Goodness and the Criterion of Truth

The existence of a good and truthful Cartesian God ensures the application of the criterion of truth. By trusting in God, we are confident not only in His existence but also in the certainty of all things we clearly and distinctly perceive. If things did not have a foundation of truth, God would give us an inclination to believe something false, which would be deceptive. Since God is perfect and cannot deceive, we can rely on our clear and distinct perceptions as true.