Rene Descartes

1. Rene Descartes 1641

2. I think therefore I am – Cogito ergo sum • Ex nihilo nihil fit – Nothing comes out of nothing • If you would be a real seeker after truth, it is necessary that at least once in your life, you doubt, as far as possible, all things

3. Why does Descartes doubt what he knows? (leads to idea of Foundationalism) • Why does he doubt his senses? • Why does he bring up dreaming? (allows you to clarify that the argument is not just that we can’t tell the difference between dreaming and waking, usually students’ initial response, but that dreaming offers a model for the idea that our conscious perceptions can be radically mistaken) • What is the difference between the dream argument and the evil genius hypothesis? • What does Descartes determine he knows for certain even faced with the possibility of an evil genius? Is he right about this? • How does the Cogito offer a model for clear and distinct ideas (certain knowledge)?

4. The dream argument • “The dream argument claims that we have no way of determining conclusively at any moment whether or not we are dreaming. Hence, it is possible at any given time that we are dreaming. Descartes thinks that this mere possibility is sufficient to undermine knowledge. Why? The most likely reason is that Descartes assumes something like: if we were dreaming, then beliefs about the external world produced in us by our dreams would tend not to be true.”

5. The evil demon • “The "evil demon" hypothesis states that all one knows for sure is that they exist (I think therefore I am). All else can conceivably be the result of input from an evil demon who just wants to mess with us. We may not really have a body or senses (think the Matrix). However, the one thing that can not be an illusion or false input is the fact that one has thought... existence of some sort. It is important to note that in the second part of his hypothesis, he refutes the existence of such a being. He puts forth the assumption of a God, who being God is all merciful and would not allow such a being to play such tricks. Thus, we can be certain that we are as we perceive ourselves - assuming we believe in God.”

6. Descartes tried to build a system with which one could attain certain knowledge about the world. Where do you think he derived his system from? • He was a mathematician and so he saw that the perfect truths of mathematics were a good place to start building this system. • Example of a building of various types of materials • Descartes started by taking off, stripping away all knowledge that he was so certain was not certain. Why? In order to reach to the true foundation, the basic blocks. This he called …

7. Descartes’ method of doubt This method begins by doubting everything that you can possibly doubt. And whatever is left is known to be certain knowledge. Is it ever possible to doubt everything you hold on as your beliefs? So Desecrates knowing he could not do that, grouped his beliefs by their origin or kinds of beliefs. He called the origin of the beliefs the foundation for the beliefs. If you could doubt the foundation, then all of beliefs held by that foundation were considered not true. In this way, he begins his analysis.

8. Argument of perception • Descartes starts by saying that he has often been fooled by his senses • - things have looked a way that they are not; things in the distance look small; sticks half-submerged in water look bent; and so on. • What we see and hear must be true, for how can we see and hear falsely? Sometimes we may hear what appears to be the voice of a good friend behind us, turn around, and discover the voice is in fact of a stranger. Did this ever happen to you?

9. Also, what about perception and dreams, Desecrates asks. Most of us have had dreams that appeared real while in the dream. • So how then can we know that we are dreaming while we are dreaming? By what mark, what indicator can we always count on to inform us of our conscious state? There is no such indicator or mark. • Therefore, you can not be certain whether you are now hearing me teach you or I am dreaming I am doing that. It must then follow that all that my senses inform me may be an illusion. • His conclusion is that, all beliefs founded by the senses cannot be known to be true.

10. Argument of the evil genius • In order to take his scepticism to the extremes, Descartes suggests that God does not exist and that all our experiences are a product of this evil demon who wants to deceive us. • Why was a demon necessary for Descartes. The possibility of the demon means that it is possible that even if I could tell the difference between being awake and dreaming, my experiences when I am awake are no more real than when I am dreaming.

11. What Descartes was doing 35o years ago was paint a picture of the Matrix. (in which the machines are feeding humans with false perception). • His theories are suggesting we cannot be certain about anything. • He himself came later to say this : Cogito ergo sum – I think therefore I am. IF every thought in his head was false at least he know he could think of that.

12. Then Descarts considered the idea of God. His argument is that since it is possible to think of a perfect being, he suggests that this idea should be an innate idea. He concludes that God exists. • If all our perceptions of this Being is that he is perfect and all aspects of this being are perfect, there is no reasons for God to deceive us. Supports the truthfulness of God.

13. Body and Soul • Descartes suggests that we have a body and soul (dualism) and that God can create one without the need of the other to exist. • These ideas have been at the heart of the philosophy of knowledge - epistemology and of course psychology. • Can a machine that perfectly resembles a human be counted as human?