I exist. What I understand clearly must be true. I understand certain ideas clearly. I understand the idea of perfection therefore a perfect being must exist. I understand God to be a perfect being. Therefore God exists.
I’m not certain of the historical significance of Meditations on First Philosophy but I think this is where Descartes’ “I think therefore I am” comes from. In this book, Descartes tries to reason about knowledge and understanding from first principles does so over six meditations. This is among the hardest books I’ve ever read, comparable to Zen and the Art of Motorcycle Maintenence, Siddartha, and The Brothers Karamazov. I read this book twice before writing this review because after the pass of superficial reading (see my report on How to Read a Book) I knew I didn’t understand most of Descartes’ arguments. I still don’t have a clear picture of his reasoning but I think his ideas are interesting.
It’s not clear to me if Descartes’ did all of this reasoning over six consecutive days or a much longer time period but he structures the book as six meditations. In the first meditation he casts doubt on everything he knows in an attempt to start from nothing. In the second meditation Descartes supposes the non-existence of all things whose existence has doubt. From here he starts building ideas the way a mathematician builds proofs and discovers how the mind and body are separate and explores the idea of substance. The third meditation reveals the existence of God. Next, Descartes explore truth and falsity and the error of judgement. His fifth meditation explores the nature of things of substance (material things) and again makes discoveries about the existence of God. In his final meditation we learn about the distinction of mind and body.
Our senses are imperfect and deceive us constantly. Our perception of something when we are far away (say a tower) may not be accurate. Its height, its shape, its color may be different once we’re up close to it. It is prudent to cast doubt on those who have deceived even once for they may deceive us again. Even in our dreams we experience our senses as if awake. How can we be sure that we are awake right now? There are no signs to distinguish reality from dreams (although we find out later in the sixth meditation that there is a sign, memory). It is better not to assume a good God but one that is deceitful and who aims to trick you in every way possible.
Knowing the Mind
Assume that everything you see and feel and touch and experience is false. How can you know you exist? Simply making this assumption of falsity means you must exist. If there some God out there deceiving you, then you must exist in order to be deceived. If you think, you are. For as long as you think, you exist. Thought is inseparable from you. From your mind. If you were to stop thinking, then you would cease to exist. You are a thinking thing. This is the great conclusion of this meditation.
An idea, considered by itself, cannot be false. Unicorns don’t exist but, with reality put aside, an idea of a unicorn cannot be false. All effects have causes. The reality of an effect must come from the reality of its cause. Something cannot come from nothing and what is more perfect (has more reality) cannot come from something less perfect. You cannot have the idea of heat or love unless that which created also had those ideas in its reality. There cannot be an infinite regression of causes and thus there must be some root cause. Some thing which contains all the reality of you. Because you are a finite being yet can imagine an infinite being, something which contains the reality of infinity must have created you. God is an infinite being. God must exist. God cannot be a deceiver. He can have the power to deceive, however the will to deceive is antithetical to the idea of this supremely perfect being.
Truth and Falsity
You only make mistakes when you judge. You got your capacity to judge from God, however your capacity is finite. If you had an infinite capacity for judgement you would never make mistakes but this is not the case. You make mistakes because you are finite. Because you are finite you will never be able to understand the will of God and it makes no sense to question His will or actions. Judgement comes in two parts: knowledge and the free will of choice. Your capacity to choose is larger than your capacity for knowledge. Because of this, you sometimes make choices on things which you do not fully understand and this is when errors happen.
Some ideas exist independently of your mind. Ideas such as a triangle which can be described by certain immutable properties like: it’s internal angles sum to 180 degrees and it’s longest side is opposite its largest angle. However, because you can think of a triangle does not one materially exists. Because you can think of mountains and valleys (which are inseparable ideas), it does not follow that mountains and valleys exist. God and existence are also inseparable ideas (perfection and existence are inseparable) and from this it follows that God must exist.
Mind and Body
Imagination and understanding are different. You do not need one for the other. Imagination is not a part of the essence of your mind for without it you would remain the same entity. You are a thinking thing yet hold a clear but distinct idea of your body. You are not your body. God is not a deceiver and He is the one who gave you your capacity to sense. To feel and see and taste. Therefore, corporeal things must exist. Yet you and your body are a single thing. You sense pain when you are injured instead of observing the injury intellectually. How is it that your senses, which are given to you in the likeness of God, in the likeness of perfection, can deceive you? How can someone drink poison when they’re thirsty? For the same reasons that other errors occur: your capacity of choice is larger than your capacity of knowledge. You are a finite being and errors are to be expected.