Descartes’ version of the Cosmological Argument is referred to as the stronger of his two arguments. There are countless different cosmological arguments for the existence of God, dating back to the ancient Greeks. Some types are still being debated today. What these arguments have in common is a reference to the principle of causality. It is fundamental to these arguments to understand this principle, which states that everything that exists must have a cause. In the special case of Descartes, he twists this widely accepted principle into something less obvious, which he calls the principle of causal adequacy.

The principle of causal adequacy states that the cause of something must have at least the same level of reality as the effect (the thing it causes). This probably makes no sense, and I wouldn’t blame you. But if you remember the ontological argument’s perception of God as a perfect being, it might be a little clearer. Let me explain. Descartes argued that everything in the world had different levels of perfection, or reality. God, obviously, exists at the top of the pyramid—with the highest level of perfection, and therefore, reality. Things like (human) minds and matter have less reality, and finally, modifications of human minds or matter have the least reality. This type of reality is referred to as formal reality. God is known as an infinite substance with the most formal reality, human minds and matter are known as finite substances, and the modifications of finite substances are known as modes, with the least formal reality. The exact terminology is not particularly necessary to the argument—just the fact that God has the maximum reality, and we have a lesser state of reality.

But wait. There is another distinct type of reality, which Descartes calls objective reality. Objective reality is the reality of the things in our ideas. So, for example, the idea of God has high objective reality because it represents a supremely perfect, infinite being. An idea of a person, or a fence, on the other hand, would have a lower degree of objective reality, as those things—person, fence—have a lower amount of formal reality. Key to our understanding is the relationship between formal and objective reality. Descartes posits that the cause of an idea must have as much formal reality as the objective reality of the thing inside the idea. This is very, very difficult to wrap your head around. I will try to help with an example. Let’s assume we have a tree and an idea of a tree. The tree is a finite substance: made of matter. The idea of the tree has the same amount of objective reality as the tree has formal reality. Since the finite substance of a tree has at least the amount of formal reality as the idea of a tree has objective reality, this is in accordance with Descartes’ proposed relationship.

Now that we have that out of the way, we can get into the argument. Remember, this proof takes place after Descartes proved that the only thing he could be sure of, at first, was his mind. From that conclusion, Descartes goes on to prove the whole world, and the Cosmological Argument is a crucial step. Descartes knows that only his thoughts can be trusted, and he clearly has an idea of God in his thoughts. However, he also understands the principle of causality, where every effect (such as the idea of God in his mind) must have a cause. God, as mentioned above, is a supreme, perfect being. This means that the objective reality of God in Descartes’ thoughts must be the maximum objective reality achievable. Therefore, since the cause of an idea must have as much formal reality as the objective reality of the thing inside the idea, a being with maximum formal reality must exist. This being, Descartes posits, is in fact God himself. Convincing, right?

The first problem I see with this conclusion is that although thought proves Descartes’ existence, it does not necessarily mean that those thoughts are reliable. In fact, I think that it is somewhat contradictory to infer an idea into the existence of God. What I mean by this is that, despite what Descartes claims, the origin of God did not originate within him. While he may have a deep spiritual connection to God, I would argue he (or anyone else) was not born with the innate belief in God. He was taught of God’s existence by someone externally, most likely when he was very young. If Descartes was in fact committed to his principle of radical doubt—where he doubts everything about the outside world besides his existence—then it is illogical to have the innate idea of God as a premise of this argument. Descartes said himself that he could not trust anything besides the fact that his mind had thoughts. But those thoughts are grounded in Descartes’ lived experiences, which he must doubt if he is sticking true to his principles.

This is not the only objection to Descartes’ theory. David Hume and Immanuel Kant both had separate qualms with Descartes’ argument. Hume, being an empiricist, pointed to the limits of reason. A classic example which exemplifies Hume’s concerns would be waking up to find your lawn is wet. Let’s assume you have no sprinklers. You might reason, in a perfectly logical way, that your lawn is wet because it rained. But that’s not the only way your lawn could be wet. Someone could have peed all over your lawn, or spat on it until it got wet. The point is: just because something seems like the logical cause for an observed effect does not mean it is the cause. Hume would challenge the principle of adequate causation—the idea that we can ever 100 percent determine the causes of things that exist. We only observe events following one another, not a causal connection between them. Causality is an association, not something we can deduce.

Kant, on the other hand, thought that the Cosmological Argument reduced to nothing more than the Ontological Argument—and had the same problems. He argued that the same problems with the Ontological Argument—that of existence being a trait—were premises of the Cosmological Argument. Kant stated that existence is not a quality or trait of a being, so therefore Descartes could not assume that because God is perfect, he exists.

There are many other versions of the Cosmological argument, and maybe I’ll learn them and write about them here.