Think by Simon Blackburn Chapter 1b Knowledge
According to A.C. Grayling, if cogito ergo sum is an argument, it is missing a premise. This premise is: A. Everything that exists thinks. B. Everything that thinks exists. C. Everything both exists and thinks. D. Everything either thinks or exists.
Descartes ultimate aim was to prove that we can only know ourselves as thinking things and nothing else. A. True B. False
Reminder of what Descartes was trying to do. Descartes was trying to put human knowledge on a firm foundation. Ultimately he hoped to be able to prove that the majority of things that we believe at a common sense can be proven correct.
Problems with the cogito argument itself The cogito argument is actually very simple to troubleshoot. Put formally, the argument is this. 1. I think. 2. Therefore, I exist. It is true that if I think (e.g., by doubting my own existence) then I must actually exist. But the real question at issue is whether there really is an I, a particular, stable entity, that thinks.
Reformulation We could reformulate Descartes argument along these lines: 1. Thinking is occurring. 2. Therefore, a thinking thing exists. Now the premise is clearly true, but, as we just showed, the conclusion may still be doubted.
Recap So Descartes famous cogito argument: I think, therefore I am. is actually not a proof of his own existence as a thinking thing. What Descartes has plausibly shown us that we can not doubt that thinking is occurring while we are actually thinking. So an evil demon could not make us think that thinking is occurring when it really isn t.
Descartes successfully establishes that A. he exists as a thinking thing. B. there is no evil demon. C. an evil demon could not make him think that thinking is occurring when it is really not. D. he ceases to exist when he is not thinking.
Foundations of knowledge Descartes aim in using the method of doubt was to find something that was beyond all possible doubt, that could serve as the logical foundation of all of our other beliefs. So, even if we were to grant that Descartes has proven his own existence beyond all possible doubt, this seems like a fairly small accomplishment. The question remains: How could he use this one fact to deduce the basic reliability of our senses?
Clear and distinct ideas In the 3 rd meditation Descartes begins the task of retrieving the world that he has succeeded in doubting away. He does this by asking what it is about the cogito argument that he finds so utterly compelling, and he decides that he has a special clear and distinct perception of its truth. (p.33).
An example In an attempt to convey the notion of clarity and distinctness, Blackburn considers the following example (p. 33). Suppose you like playing with geometrical figures, and you ve noticed that anytime you draw lines from the opposite ends of the diameter of a circle and connect them somewhere on the circumference, they seem to meet at right angles like this:
Example (continued) Well, it s one thing to notice that this seems to happen, but it s a completely different thing to know that it happens. How can we really be sure it s not an accident of some sort? The proof is actually pretty sweet. If you draw a line from the radius to the (allegedly) right angle, you create 2 isosceles triangles, since two sides of each of the smaller internal triangles are the exact radius of the circle.
Example (continued) So the angles indicated are equal. But since we know that the internal angles of a triangle sum to 180 degrees, we know that A + A + B +B = 180. So, 2A + 2B = 180 So, 2 (A + B) = 180 So, (A+B) = 90. Eureka!
Clarity and distinctness This example seems to make clarity and distinctness something that would only apply to the intellect, but Descartes talks about clear and distinct perceptions as well. But how do we know that our clear and distinct perceptions can be trusted? What happened to the evil demon?
God Descartes makes a pretty breathtaking move at this point. First, he attempts to banish the evil demon by proving the existence of God as a perfect and benevolent being. Then, he attempts to prove that a perfect and benevolent being would not give us clear and distinct ideas unless we could rely upon them. In other words, if God made us believe that clear and distinct ideas were reliable when they aren t, that would make him a deceiver, in effect the evil demon Himself.
The Cartesian Circle This is where many people think that Descartes commits a serious error in reasoning. The basic problem is this: In order to show that we can trust our clear and distinct ideas, we must first know that there is a God. But in order to show that there is a God, Descartes relies on the claim that he has a clear and distinct idea of God.
Circular reasoning 1 Circular reasoning essentially amounts to assuming the very thing you are trying to prove. For example, if I wanted to prove to you that George Clooney is my brother, it wouldn t be very convincing to you if I tried to do this by claiming that his mother, the famous singer Rosemary Clooney, is also my mother.
Circular reasoning 2 You are unconvinced because even though you know that Clooney and I would have to be brothers if we had the same mother (or at least half-brothers), you doubt that Rosemary Clooney is my mother just as much as you doubt that George Clooney is my brother. In other words, my argument just assumes the truth of the very thing I am trying to prove.
Descartes Circle Descartes has the same problem. He can t prove to us that clarity and distinctness is a reliable condition by telling us something (i.e., that a perfect God exists) that simply assumes that clarity and distinctness is a reliable condition.
Descartes believes that his clear and distinct ideas can be trusted because A. if they could not be trusted, God would be a deceiver, which he is not. B. he has faith in God s existence. C. he has vast experience with them being trustworthy. D. he has already proven his own existence using these clear and distinct ideas.
The Cartesian Circle is the problem that: A. Descartes can t prove that God exists. B. Descartes proof that we can trust clear and distinct ideas seems to simply assume that we can trust clear and distinct ideas. C. Descartes proof that we can trust clear and distinct ideas is not itself as clear and distinct as we would like.
The rationalist s dream We indicated earlier that Descartes was one of the greatest mathematicians of his age, and proofs like this were child s play to him. But it s fair to say that his conception of true insight comes from his experience with higher mathematics. Blackburn indicates that this is the dream of rationalism. In philosophy, a rationalist is someone who believes that all human knowledge can be demonstrated on the basis of reason, and reason alone. Knowledge of this sort is known as a priori knowledge, which means that it is gained prior to, or without the aid of, experience.
Rationalism vs. Empiricism In the introduction we were introduced to the word empirical, which means based on experience. These are the two opposing points of view in the study of knowledge: Rationalism: knowledge is based on reason. Empiricism: knowledge is based on experience.
Hume s Critique About 80 years or so after Descartes died a Scottish philosopher named David Hume provided a crushing critique of Descartes methodology. (p.40) Hume s critique of Descartes method of doubt is essentially just that it is doomed to fail from the beginning. For, even if we find something like the self that is indubitable, we will never be able to advance past that, because we are still doubting all the basic principles of reasoning that might be used to do so.
Rationalism vs. Empiricism again Hume trusted reason, but he rejected rationalism. For Hume, the only way we could ever come to know anything about the world is through experience. This makes him an empiricist.
Descartes vs. Hume Everybody knows that both reason and experience are required for knowledge in an ordinary sense. Hume and Descartes understand this, too. Their debate is about the ultimate foundation of knowledge. Is the trustworthiness of experience ultimately based on reason? Or is the trustworthiness of reason ultimately based on experience?
The difference between a rationalist and an empiricist is: A. Rationalists believe in reason, but empiricists believe in experience. B. Rationalists believe that the foundation of knowledge is reason, but empiricists believe that the foundation of knowledge is experience. C. Rationalists believe in the Cartesian Circle, but empiricists reject the Cartesian Circle. D. Rationalists are foundationalists, but empiricists like Hume question the very possibility of a foundation for knowledge.
Problems with foundationalism Hume and Descartes actually agreed that knowledge requires a foundation. They just disagreed on what sort of foundation could be supplied. But Blackburn points out (p.44) that some philosophers disagree with the whole foundationalist perspective. This is best captured by the famous quote from Otto Neurath: We are like sailors who on the open sea must reconstruct their ship but are never able to start afresh from the bottom. Neurath s analogy captures Hume s point that it s really impossible to doubt everything at once. But he takes Hume s point further by claiming that establishing a foundation for all of our knowledge doesn t make any real sense.
Coherentism Philosophers who reject foundationalism are often called coherentists. Coherentists basically believe that knowledge is not a matter of our beliefs all resting on a firm foundation. Rather, knowledge is a matter of our beliefs fitting together or cohering in an optimum way.
Problems with coherentism Coherentism is based on kind of a jig-saw puzzle analogy. But the analogy is problematic because we don t have any assurance that there is one best way for our beliefs to fit together. If there are multiple way that our beliefs can fit together, but only one way that the world actually is, then its hard to see how coherentism can be right.
Brains in a vat 1 A contemporary version of Descartes evil demon argument is the brain-in-thevat argument. A philosopher named Hilary Putnam asked How do you know that your aren t just a brain in a vat? The idea here is that it s logically, and perhaps even technologically possible that your brain was removed from your body at some point in your life, immersed in a nutrient bath, then wired up to a computer so that it continued to have all the experiences you had when it was in your body.
Brain in a vat 2 You ll notice that the brain in a vat argument isn t based on Cartesian doubts about the existence of the physical world. Brains are physical things. The argument establishes that even if the physical world exists we could be completely wrong about the sort of physical thing we are.
Boltzmann Brains Blackburn ends this chapter with another skeptical argument produced by Bertrand Russell (p. 46) You may be surprised to find out that this question disturbs physicists quite a bit. Today it is discussed under the concept of the Boltzmann Brain, which you might want to Wikipedia sometime.