A Summary Of The Meditations
Meditation 1: On the things that may be called into doubt.

In which Descartes introduces his project of building a new edifice of scientific and philosophical knowledge using his method of doubt. Neither the senses nor reason can be trusted so long as it possible that we are mistaken about their deliverances. We are familiar with everyday errors in perception and this should suggest, in this extreme philosophical enterprise, that we reject the evidence of the senses entirely, since they are not infallible. Yet there is surely a difference between a local mistake, such as seeing a square tower as round in the distance, and a global mistake, which would be when everything we experience is mistaken. But since any veridical sensory experience could be reproduced as a dream, if there is no means of distinguishing dreaming from wakefulness, we cannot be sure whether experience faithfully reflects a world beyond the mind or not. The dreaming hypothesis would leave knowledge of such things as mathematical truths alone, for they are no less true in dreams. Yet if there could be an malicious demon with full control over my mind, then he could deceive me constantly, for the certainty that naturally attends even the simplest of thoughts, such as that 2+2=4, could be nothing more than his making me feel certain. It therefore appears I can be certain of nothing.

Meditation 2: On the nature of the human mind and that it is easier to understand than bodies.

In which Descartes establishes his Archimedean point of certainty, the Cogito and shows that, contrary to common belief, we know the mind better than we know the world around us (assuming that there is one). Regardless of how cunning the demon is, he cannot make Descartes think he does not exist, since the apprehension of that thought will make one aware that one is thinking it. Hence one cannot fail to be certain that one exists just when one is thinking. Descartes knows he is at least a mind – a thinking thing. To think in this extended sense is not merely to cogitate but to have any kind of mental act. The distinctness of mind and body is revealed, as mind is not extended and body is; yet Descartes admits he cannot yet tell whether this is a real or merely conceptual distinction. By bringing a piece of wax near a fire, Descartes argues that bodies are not perceived by the senses but by the intellect. The wax loses all the sensible properties it had and gains new ones. If it were nothing more than the sum of these properties, we would have to conclude that one object had been destroyed and another created. The intellect understands the essence of body to be spatial extension, which is preserved (if modified) over the change of sensible properties.

Meditation 3: On the existence of God.

In which Descartes establishes the principle that anything which can be clearly and distinctly perceived by the natural light of is true and uses this to establish that God exists. Descartes finds himself with an idea of God. What is the cause of this idea? A cause must have as least as much reality as its effect. Since Descartes or any other finite being has less finite reality than God, only God could be the cause of his idea. So God must exists. Descartes then wonders, by way of continuation, whether he could exist with his idea of God if God didn’t exist? He argues that he could not have brought himself into existence, for only a perfect being could do this and he recognises that he is not perfect. He could have been brought into existence by his parents, but this merely forces us to ask how they came into existence. Eventually, we will need to recognise a being with a higher degree of reality. So God must exist to be the cause of our existence. As for the idea of God, we know it can’t be an invention of my mind. It could be something I have picked up from others but this too forces the question of whether they got it from. Descartes concludes that we are born with the idea of God. God himself places the idea in us as a craftsman puts his mark on his work.

Meditation 4: On Truth and Falsity

In which Descartes investigates how it is that we can make mistakes. Since God is perfect, he cannot be deceiving me. For the same reason, he could not have given me some faculty of making mistakes (such as misjudging or misapprehension). Similarly, nor could have he given me imperfect faculties for detecting the truth. Finally, it must be in God’s power to have made me such that I never erred. Yet I do make mistakes. How is this? It is because of a difference between the understanding and the will. When I consider, I exercise my will, for I must choose what I am to judge and want to do it and then my understanding, in making the judgement. So long as I use my understanding correctly, I will never make mistakes, for God has given me a faculty of clear and distinct perception. Mistakes arise when my will extends beyond my understanding: when I make a judgement without subjecting what I am judging to my understanding. This is what occurs when we jump to conclusions, trust appearances, and choose without thinking of the consequences, for example. Should we say that God’s error lies in giving me such a will? No, for God has given us free will, which is a sign of his benevolence, and free will does not come in degrees, so it is not as if he could have given us two faculties, the understanding and the will, whose limits exactly coincide.

Meditation 5: On the essence of material things and the existence of God once more.

In which Descartes finds the essence of material things to be extension, this train of thought leading him to another proof of God’s existence, and explains finally the role of God in his philosophy. Descartes reflects on how he can discover truths by examining the essence of things, regardless of whether they exist. Yet God is such (and the only such thing) that necessary existence belongs to his essence. So reflection on God’s essence shows that he exists, necessarily. (Descartes warns us not to not to think that God’s existence depends on our reflecting on this.) Observing finally how it is not evident that the square of the hypotenuse of a right-angled triangle is equal to the sum of the squares of the other two sides, Descartes remarks that once discovered, it should be that we do not need to go over the proof each time to know this. So long as we have just clear and distinct perception as a touchstone for truth, we could not avoid doing so. If we have proved the existence of a benevolent God, then we have greater security. A conviction that a certain truth is evident because we have once proved them is grounded by His existence. In other words, we don’t need to worry about an evil demon constantly fooling us. We can therefore engage in the practice Descartes calls science.

Meditation 6: On the existence of material things and the real distinction between the mind and the body.

In which Descartes establishes the distinction between mind and body, investigates their nature and concludes that he can know he exists in a material world of other things. I have a faculty of imagination, which presents ideas spatially, as opposed to the faculty of the intellect, which does not. We can illustrate their distinctness by noting that I can conceive of a chiliagon but I cannot imagine one. Imagination requires a body, intellection does not; hence, imagination is not part of the essence of mind. The distinctness of mind and body is shown by the fact that if I can clearly and distinctly perceive X existing independently of Y, then X must be independent of Y, for it would be contrary to God’s power not to be able to make it so. I can conceive of mind without body and vice versa. For mind is indivisible and body is divisible. Neither substance depends on the other. I am a union of mind and body. I am not simply informed of damage to my body when I step on a pin. I experience it as a pain. Do now my senses faithfully depict an external world? My senses may often let me down but we have explained the source of error and that God is not a deceiver. So my senses are right in reporting an external world but I must be careful in judging whether they report the nature of things correctly. With knowledge of mind, body and God, I can reject the extreme doubts that started me off and pursue the enterprise of genuine scientific discovery.