One of the first ideas in philosophy people often hear is Descartes’ famous Cogito, Ergo Sum: I think, therefore I am. In this post, I’d like to dissect the phrase, offer its true meaning, and challenge Descartes on its overall implications for knowledge.

I’ve discussed earlier in this blog how Descartes arrived at this landmark conclusion. However, it’s worthwhile to go over it again. In pursuit of true knowledge, Descartes began to question everything. He doubted people, himself, and the entire world around him. Eventually, Descartes’s radical doubt led him to conclude that the only thing he could be sure of was that he doubted. He took this view and used it to form the conclusion: I think, therefore I am.

But wait. In proving that he “is,” Descartes seems to have invoked some form of other knowledge. Can you find what it is?

The leap is in the therefore. I think, therefore I am sounds good, but it could just as easily have been translated to I think, for that reason, I am. Let’s unpack this carefully. Descartes is basically arguing:

1. I doubt, meaning I think.
2. Thinking is a characteristic of a being, i.e., something cannot think without existing.
3. Because I can think, I must exist (or I am).

Where Descartes only includes two premises for simplicity, there really should be three. The middle one is often implied, but it is needed for the sake of this argument. What Descartes exhibits above is a form of logic. If we replace the statements above with variables, the argument can be restructured as

1. a
2. a necessitates b
3. b.

Where a is thinking and b is existence.

Now, it sounds so silly to bring up, but if we are really committed to finding true, undoubtable knowledge, why do we just assume the veracity of this logical structure? Is logic itself outside of the realm of doubt? A true skeptic should question, “why do we trust modus ponens at all?” Since Descartes’s most fundamental proof of existence hinges on the (implicit) fact that reason is a valid form of knowledge, it seems we are stuck. We can (a) accept that logical intuition is a valid form of knowledge, and therefore also prove that we exist, or (b) reject logical intuition as a form of knowledge, and then be forced to discard Descartes’s revolutionary conclusion. There seems no easy way to go here. If we are to prove that Descartes’ conclusion remains true, we are practically forced to admit that logical truths are ingrained into the real world. If even the Cogito isn’t indubitable, then Descartes’ entire project of finding a foundation for knowledge may have been doomed from the start. Of course, we could argue that logic is something created by humans. But in doing so, we then admit that logic is something we very much can doubt—which is what I have been trying to show with this paper.

I think that this forces us into the conclusion, in a nearly indisputable way, that logical validity, while coined by humans as something called “modus ponens” or “modus tollens,” is a structure of thought that is impossible for us to escape. In fact, it is so deeply buried into our hardware that we don’t bat an eye even when it forms the bridge of a supposedly indubitable argument. Of course, Descartes himself would refute this argument. He would insist that the jump from I think to I am is already known, intuitive, and therefore grasped together in a single truth that is not mediated by logic. But I think this is silly. Even if they are “grasped together,” that is just further proof that logical thought is so ingrained into our “system of thinking” that it becomes difficult for one to even distinguish that there is something in between in the first place.