How Descartes Proves the Existence of God in Meditation III

In Mediation III, Descartes attempts to prove the existence of God. Descartes is certain that he is a living thing, a thing with thoughts and ideas, however God could be deceiving him. Thus, he digs deeper to learn more about God and his existence to assure himself that he is not being deceived. Descartes divides his proof into three steps.

In the first step, Descartes distinguishes two kinds of reality; formal and objective reality. Formal reality is what a thing is. Everything has formal reality. Objective reality is what it refers to, thus things with referential value, such as signs, words, ideas and symbols. For example, if I have an idea of flower, there are two realities to it. The formal reality of the idea of flower is an idea, and the objective reality of the flower is the actual flower to which it refers. In the second step, Descartes describes the hierarchy of being. In this hierarchy of being there is an infinite substance and the mode. This order goes from most real to least real. Substances are more real than modes because substances are independent upon modes and modes are dependant upon substances. Infinite means unlimited and finite means limited. Humans are finite substances and therefore our knowledge is limited. However, if an infinite substance exits, it has unlimited knowledge.

Lastly, in the third step, Descartes explains the causal principle. For the ideas that are coming from the outside (adventitious ideas), there must be something that is causing these ideas and bringing them into the mind. The causal principle is a principle where the cause of an effect must have at least as much reality as the effect. The cause of an idea must have at least as much formal reality as the idea has objective reality.

An example to prove the causal principle would to take 3 things from Descartes’ mind and to apply units to them. For example, in Descartes’ mind there is the idea of the color blue, the idea of a horse and the idea of an infinite substance. They all have the same formal reality because they are all ideas. However, in terms of their objective reality, they do differ. The objective reality of the color blue is 5 units, the horse is 7 units and the infinite substance is 10 units. What kinds of things outside the mind are the causes of these ideas? For blue and the horse, it is possible that Descartes has seen the color blue and the horse, that a mode is responsible because it works mathematically; because of 5 and 7 units of formal reality. But it is also possible that a finite substance (Descartes himself) is the cause and he came up with it. It is also possible that an infinite substance put it into his mind because the infinite substance has more units (10). However, for the infinite substance, seeing a mode cannot be the cause of seeing the infinite substance; the number do not match up, 7 is smaller than 10 and therefore Descartes could not have come up with the idea himself. The idea therefore