Descartes uses epistemology and metaphysics to frame his famous “cogito” argument. But in order to understand how that works, first, we must discuss the differences between an epistemological and a metaphysical question. Epistemology is a facet of philosophy interested in knowledge. And an epistemological question is a question concerned with something relating to knowledge, apprehension of knowledge, knowledge-world correspondence, or the origins of knowledge. What is knowledge? Is knowledge even possible? If so, how do we get it? Does knowledge correspond to reality?
How do people acquire knowledge? –Is it from the world or from our experiences in the world or do we have it before we experience the world? Metaphysics is a division of philosophy interested in figuring out exactly what being is. Basically any kind of question about what is, natural or supernatural, including science and religion, is a metaphysical question. Some of their perennial questions are what is the difference between particulars and individuals? Is there a reality out there? What is reality? Is there a god? What is god? Is free will a possibility?
Is change possible? What is identity? How much control do agents have control over their actions? And though these two philosophies overlap in some places, they have three major differences. First, epistemology is almost always focused on being a living thing, because even if one investigates whether or not knowledge corresponds to the world, an agent is still necessary to see uncover the knowledge there. Second, metaphysics is very often focused on the differences between things, and while you could ask the question “Is there such a thing as knowledge? in both an epistemological and a metaphysical context, your answers could be very similar, but will likely be different. They’d differ because epistemologically, asking the question will usually break down into questions about the justification for beliefs and knowledge; whereas a metaphysical question will focus on locating the conditions to declare knowledge existent. Third, epistemology with very little exception is focused on human beings; metaphysics in its very nature is about everything including human beings.
But, metaphysics and epistemology have a lot of similarities. One particular way both epistemology and metaphysics can be approached is mind/pure thoughts and body/material being. And this is how Descartes approaches it in his cogito argument. While looking for the ultimate grounds of knowledge, Rene Descartes came into despair because nothing seemed grounded and it was as if the Empiricists had won. But then a brilliant revelation finally dawned on him: no matter what, in order to have any experience–in order to be–he must think.
He says that even if it’s the case an evil deceiver made up the universe just to trick us, and everything we’ve ever known is an illusion, we must exist as thinking things in order to be deceived (otherwise we wouldn’t be able to be deceived–things that can’t think, e. g. rocks, can’t be decieved). In fact, if I didn’t think I couldn’t do anything or have any experience–I wouldn’t exist! Descartes’ method uses a very interesting train of logic. First, he takes a metaphysical stance: nothing is real. Next, he looks for things he can trust as real.
This step uses epistemology (systematically verifying the contents of his knowledge) to ground a metaphysical question (what is real? What am I? ). (So, it’s not a big surprise he ended up finding an epistemologically grounded first truth. ) Finally, he uses a thought experiment, the evil deceiver, to uncover his first truth: I must think in order to exist. Once he formulates the cogito, he uses it to argue the metaphysical point that mind is separate from the body. After all, thoughts aren’t tangible, temporal, or destructible, whereas a body and things in the world are in space, exist in time, and can be destroyed.
So, because of this, he makes a sharp metaphysical distinction between the mind and body, leaving philosophic room for religious beliefs like the afterlife and answering some questions about the mind. So, for Descartes, what I am is a thing that thinks because epistemologically, there can’t be thinking without an agent to think. (And by thinking, Descartes really means understands, grasps things, has beliefs or knowledge. ) Because of this, he thinks that I am separate from my body, which is a metaphysical claim. So, his idea of mind-body dualism needs both metaphysical and epistemological claims in order to function.