Doubt and certainty › The Existence of God

The Third Meditation addresses a fundamental problem. Descartes has established that he exists as a thinking thing. But how can he escape the prison of his own mind? How can he know that anything exists beyond his thoughts? Descartes' strategy is to prove the existence of God. If he can establish that a perfect, non-deceiving God exists, then he can trust that his clear and distinct perceptions are reliable, since a perfect God would not allow him to be systematically deceived. The argument proceeds through an analysis of ideas. Descartes distinguishes between the *formal reality* of an idea (the fact that it exists as a mode of thought) and its *objective reality* (what it represents or is about). A thought about the sun has the same formal reality as a thought about an ant—both are equally thoughts. Objective reality concerns the degree of reality represented by an idea. Descartes distinguishes ideas representing modes or qualities, finite substances, and an infinite substance. A sun and an ant are both finite substances; their size does not put them at different levels in this hierarchy. The important contrast for his argument is between a finite substance and the infinite God. > **The Trademark Argument** > > Descartes argues that effects cannot have more reality than their causes. The idea of an infinite, perfect being (God) has infinite objective reality. Since Descartes himself is finite and imperfect, he could not be the cause of this idea. Therefore, the idea must have been placed in him by an actually infinite, perfect being. His conclusion is that God exists; he compares the idea of God to the mark of a craftsman on his work. The argument depends on premises a reader may dispute. Why assume that the idea of infinity requires an infinite cause? Cannot we form the idea of infinity by negating our concept of finitude? Descartes anticipated this objection and insisted that the idea of infinity is a positive idea we could not have invented, rather than the negation of finitude. The Fifth Meditation offers a different argument for God's existence: the ontological argument. The idea of God is the idea of a supremely perfect being. Descartes argues that necessary existence belongs inseparably to the nature of that being. His comparison is with the properties belonging to a triangle: understanding a triangle commits us to its geometrical properties, although it does not establish that any triangle exists outside thought. Descartes claims that God is a special case because necessary existence belongs to the divine nature itself. Whether that move succeeds is precisely what an objector can dispute. This argument has been debated for centuries. Kant's famous objection is that existence is not a property or perfection that can be included in a concept. To say that God exists is not to add a property to the concept of God but to assert that the concept is instantiated. Kant develops this criticism in the [*Critique of Pure Reason*, A598/B626](https://sourcebooks.web.fordham.edu/basis/anselm-critics.asp). His objection targets the step from a concept to the existence of its object.