PHI 1500: Major Issues in Philosophy Session 13 March 17 th, 2015 Philosophy of Mind: Descartes 1
Philosophy of Mind OBen concerned with explaining the relafonship between our minds and our physical bodies, Or more generally, the metaphysical relafonship between minds and the physical world. Many philosophers, including Descartes, have offered disfncfve solufons to the mind- body problem:» the problem of specifying how the minds and bodies fit together to produce conscious agents. SoluFons to the mind- body problem generally divide into: Dualism vs. monism Dualist views, which treat the mind & body as different enffes Monist views, which say that mind & body are really the same thing 2
Our old friend Descartes (1596-1960) defended an influenfal substance dualist view of the mind. Philosophers pben call his view Cartesian dualism, to disfnguish it from other versions of dualism, which agree that minds and bodies are fundamentally different, but explain their relafonship in different ways. Some terminology: A substance is a type of stuff. E.g., water, steel, and bone are physical substances. Some people think that thoughts, feelings, and dreams must be made out of a sort of mental substance. Substances have proper7es, i.e., qualifes by which a substance can be described. ProperFes can be intrinsic or rela7onal. An intrinsic property is a feature that a substance has under any and all circumstances, independently of its relafon to other things. A rela7onal property is a feature a substance has only in virtue of how it relates to other things. 3
Types of Dualism Mind stuff One type of stuff Mental properfes Body stuff Physical properfes Cartesian dualism is a type of substance dualism: It says that minds & bodies are two dis7nct types of substances Minds are res cogitans: things that think (believe, imagine, feel emofons, etc.) Bodies are res extensa: things that are extended in space. Contrast this with property dualism, in which minds & bodies are one substance, which has two dis7nct types of proper7es: mental ones, and physical ones. (We will read a defense of property dualism by Frank Jackson next week.) 4
In Medita7on II, Descartes claimed he could imagine himself without a body, and concluded that he must be an immaterial thinking thing, not his body. He realizes, in Medita7on VI, that he does not have evidence to conclude decisively that his body really exists. but he will ulfmately argue that:» His body really does exist» His body has very different properfes from his mind.» Minds and bodies are made of different substances. 5
Existence of the Body ABer doubfng everything he has ever believed, Descartes cannot: - see that, from this disfnct idea of bodily nature that I find in my imaginafon, any argument can be derived that will lead necessarily to the conclusion that some body exists. (52) All of the evidence for his having a body, e.g.: Feeling hunger, thirst, and other such appeftes, Feeling emofons with an accompanying bodily sensafon (like joy, sadness, and anger), Sensing the qualifes of other physical things, Experiencing pleasure and pain from interacfng with other physical things came from his senses, which he no longer trusts. 6
Since starfng his MeditaFons, Descartes does not trust any sensory evidence for the existence of his body. many experiences gradually undermined all the faith I had placed in the senses. (54) He concludes: in macers of the external senses our judgments are at fault. (54) Even sensafons arising from our own bodies can be misleading! I had oben heard from people whose arm or leg had been amputated, that they sfll occasionally seemed to feel pain in the part of the body they were missing, (54)» So, he thinks he ought to doubt that his bodily sensafons correspond to real physical events. phantom limb pain 7
But, Descartes says that although I do not think that all that the senses seem to teach me is to be rashly accepted, I do not think that it should all be called into doubt. (55) Remember (from MeditaFons I & II) that Descartes is sure he cannot doubt that: God exists, God is omnipotent, God is perfect and good, God could not deceive him. Ø Descartes arguments that: a) bodily things exist, b) minds & bodies are different substances, Ø both rest upon several assumpfons about God. 8
Argument for the Existence of the Body Descartes says that God has endowed [him] with a strong propensity to believe that he has a physical body and is affected by bodily things (56).» So, if it turned out that bodily things did not really exist,» then it would be impossible to think of [God] except as a deceiver. (56) Ø One way of looking at the argument is as a Modus Tollens. 1. If bodily things do not exist, then God must have deceived us into firmly believing that bodily things exist. [If P, then Q] 2. God is not a deceiver. [Not- Q] 3. And therefore bodily things exist. (56) [Not- P] 9
Argument for the Existence of the Body An alternafve, more sophisfcated way to look at this argument is as an instance of a reduc5o ad absurdum, = a type of argument where one shows that accepfng the opposite of the claim one is defending requires one s opponent to accept another claim, which is clearly false. Descartes wants to prove that bodily things exist. He tells us that if someone believes the opposite (that bodily things do not exist), then they will have to accept that God is a deceiver.» He is absolutely certain that God is not a deceiver, so he has a reason to reject the claim that bodily things do not exist. The reducfo strategy works similarly to a disjunc7ve syllogism. 1. Either bodily things exist, or bodily things do not exist. [P or Q] 2. It is not the case that bodily things do not exist. [Not- Q]» (supported by an auxiliary argument, with the premise that God is not a deceiver.) 3. Therefore, bodily things exist. [Therefore P] 10
Argument for the Separa7on of Mind & Body This argument relies on the conceivability principle: that if you can think about something, then that thing is possible. Conversely, if you can t think about something (like a round square), then that thing is impossible. Descartes version of this principle is that If one can clearly and disanctly understand something, then God can make it so. because, if God is omnipotent and omniscient, he has the power to make anything we can think of. since I know that whatever I clearly and disfnctly understand can be produced by God such as I understand it to be, then if I can clearly and disfnctly understand one thing without another, this is sufficient for me to be certain that the one is disfnct from the other, since they can at least be produced separately by God. (55) In other words, Descartes reasons that:» If I can understand one thing without another, then God can make those things disfnct from one another. 11
Argument for the Separa7on of Mind & Body (con7nued) Next, from the very fact that I know I exist, [This was the conclusion of MeditaFon II: the one thing that he absolutely could not doubt] I rightly conclude that my essence consists in this alone, that I am a thinking thing. (55) Also, I have a body, which is very closely conjoined to me, yet because, one the one hand, I have a clear and disfnct idea of myself, insofar as I am a thinking and not an extended thing, and on the other, a disfnct idea of the body, insofar as it is only an extended and not a thinking thing, so it is certain that I am really dis7nct from my body and can exist without [my body]. (55)» Descartes is claiming that he can understand himself without his body. Can you understand yourself without your body? 12
Argument for the SeparaFon of Mind & Body 1. If I can understand something, then God can make it so. 2. If I can understand one thing without another, then God can make those things separate from one another. 3. I can understand myself without my body. 4. Therefore, God made minds separate from bodies.» What do you think of this argument? Is it valid? Is it sound? Is it persuasive? 13
Leibniz s Law Descartes argument for substance dualism rests upon the following principle, later described by the German philosopher G.W. Leibniz): If A and B have all the same proper7es, including their posifon in space, they are indiscernible from one another you can t tell them apart. If A and B are indiscernible, they are iden7cal: A = B. E.g., water & H 2 O are idenfcal. But, if A and B have different proper7es (even if they occupy the same posifon in space), we can tell them apart: they are discernible, or disfnguishable, from one another. If A and B are discernible, they must not be iden7cal: A B. E.g., water & the sugar dissolved in it are not idenfcal. 14
Descartes Use of Leibniz Law Descartes calls acenfon to many differences in proper7es between his mind and his body: The mind enables thinking, but the body cannot. The body is extended in space, but the mind is not. We are in control of our thoughts, but not our bodily sensafons. We can be deceived about our bodily sensafons, but not about our thoughts. The body can be divided into parts, but the mind cannot. The mind is part of his essence, but his body is not.» Do you agree that the mind and body have all of these differences? 15
Moreover, Descartes argues that his mind & body are different in that he could exist without his body, (since he can imagine himself without imaginafon, sensafon, or the ability to move through space) but he could not exist without his mind, since he is essenfally a res cogitans a thinking thing, made of mental substance.» Remember that the conceivability principle says that if you can think about something, then that thing is possible.» Descartes is inferring that if he can think about himself without a body, then it is possible for him to exist without one. He has already argued that bodily things do exist, And he assumes that everything that exists is made of some sort of substance, so he reasons that if indeed [bodily things] exist, they must inhere in a bodily or extended substance, which he calls res extensa. 16
At any rate, Descartes assumes as a premise that: Minds & bodies have different properfes. He also uses Leibniz s Law as a hidden premise: If two things have different properfes, they cannot be idenfcal. and infers (by Modus Ponens) that: Hence, minds & bodies must not be idenfcal. Also, Descartes assumes that if two things are not idenfcal, they cannot be the same substance, and infers that: Therefore, minds & bodies are different substances. Ø This is the central thesis of substance dualism. Another way Descartes makes this argument is that: I am made of mind substance (res cogitans), And bodies are made of physical substance (res extensa), Therefore, minds & bodies are different substances. 17
Some cri7cs have objected that Descartes has misused Leibniz s Law. Mind stuff Body stuff Descartes argued that the mind & body must be disfnct substances, because minds & bodies have dis7nct proper7es, and thus we can understand them apart from each other. But, the properfes that Descartes uses to tell them apart are not clearly intrinsic proper7es, which belong to the mind and body themselves. Rather, they are rela5onal proper5es: i.e., facts about how Descartes can think about those things, and whether or not he can doubt their existence. Video on the Masked Man Fallacy: bit.ly/1wszhhs 18
Other cri7cs say substance dualism isn t a soluaon to the mind- body problem at all, - because it fails to explain how the mind & body can interact with one another, if the body is extended in space, but the mind is not. Descartes thought that the interacfon took place in the pineal gland. He thought this must be where the soul exists, because it is right in the center of the brain. He says that all human behavior can be explained mechanisacally, as a circuit of mental causes & bodily effects. E.g., mental events (like the intenfon to point at the arrow) cause changes in the physical body (muscle contracfons that move the arm to point at the arrow) but it is sfll unclear how mental events are supposed to cause physical mofon. 19
So for Descartes, minds are ghostlike, and bodies are machine- like. But trouble sfll remains: how can an immaterial thought cause our material body to move in a certain way? Conversely, how can an event in our physical body (like ingesfng a hallucinogenic drug) cause mental experiences? CriFcs of substance dualism think Descartes has not given an adequate explanafon of how these interacfons occur. We will discuss a famous crifque of Cartesian dualism by Gilbert Ryle next class. 20