Substance Dualism The substance dualist thinks that no physical substance has mental properties and no mental substance has physical properties. Minds don’t have size, shape, location, etc. and brains don’t have moods, thoughts, pains, etc.
From the Reading “[According to substance dualism] Your body is like a probe, sent by NASA to explore a different planet. The probe sends pictures back to mission control, where scientists decide what the probe should do next. Instructions are then sent back to the probe which responds accordingly. The probe itself is entirely unintelligent” (p. 10). And it has no feelings, emotions, pains, etc.
Short Circuit When I was 4 years old, the movie Short Circuit came out. In it, a robot gets struck by lightning and becomes sentient.
Throughout the movie, various characters argue that the robot can’t be sentient (have a mind), because robots can’t _____: Things with minds can _____ Robots can’t ______ Therefore, no robot has a mind.
Robots Can’t _____ Be expressive Exhibit curiosity Engage in playfulness Speak fluidly Learn new things Appreciate beauty Expect future conscious experiences
Robots Can’t _____ Have a fear of death Act originally Enjoy dancing and music Have a sense of humor Conform to moral laws out of principle Mentally associate disparate things Exhibit spontaneous emotional responses
Similar arguments can be made for substance dualism. Instead of “Robots can’t _____,” the substance dualist argues that there are things minds can do that “No physical object can _____”: Minds can _____ No physical object can _____ Therefore, no physical object is a mind.
Is it possible for physical objects to do these sorts of things– learn new things, be creative and original, fear death, make plans for the future, experience redness…?
Descartes René Descartes (1596- 1650) was a French natural philosopher and mathematician. He is the father of modern (Western) philosophy, and he argued for substance dualism.
The Cogito Descartes famously said “I think, therefore I am” (“Cogito ergo sum”). He argued that it is not possible for him to doubt his own existence. Only things that exist can doubt.
The Deceiver But Descartes thought it was possible for him to doubt that he had a body. Sure, it looks and feels like he has a body. But couldn’t an all-powerful God make it seem like Descartes had a body, when he really didn’t?
1.I cannot doubt that I exist. 2.I can doubt that my body exists. 3.Therefore, I am not my body. 4.I am my mind. 5.Therefore, my mind is not my body
Leibniz Gottfried Wilhelm Leibniz (1646-1716), like Descartes, was a natural philosopher and mathematician. Among his many achievements, he formulated a law of logic called Leibniz’s Law.
Leibniz’s Law Also known as “the indiscernibility of identicals” If X = Y, then X and Y have all the same properties. [Converse] If X and Y don’t have all the same properties, then X ≠ Y.
Example Property: being red 1.My car is red (has the property of being red. 2.That car is not red (does not have the property) 3.Since my car and that car don’t have all the same properties, that car is not my car.
Descartes’ Argument Again Property: being a thing whose existence Descartes can doubt. 1.Descartes’ body has the property of being a thing whose existence Descartes can doubt. 2.Descartes does not have the property of being a thing whose existence Descartes can doubt. 3.Therefore, Descartes is not Descartes’ body.
No Action at a Distance At the time Descartes lived, it was commonly believed that for one object to exert a force on another, they had to contact one another. But the mind, according to Descartes, is not spatially located, has no surfaces, and no mass. How can it contact and thus affect the body it controls?
No Explanations The substance dualist has not given us an explanation for how the mind controls the body, in the way that a physicist can tell us how the mass of the various planets determine Earth’s orbit.
We Can Already Explain Bodily Movements Why did I raise my hand? Because a muscle in my arm contracted. Why did the muscle contract? Because of an electrical impulse in a nerve. Why did the nerve have the impulse? Because certain neurons in the brain fired. Why did they fire?...
Substance Dualism Violates the Laws of Physics Physics says that the motions of particles are completely determined by the physical forces that act on them (the strong nuclear force, the electro-weak force and gravity). If a non-physical mind exerts a non-physical force that changes the motion of ANY particle in your body, then physics is wrong.
Unconscious Mental States Philosophers used to think that all mental states were conscious. If you thought that, then you could say that consciousness is just part of being in the non-physical mind. But now we know there are unconscious mental states. How can the substance dualist explain what makes some mental states conscious and others not?
Brain Damage According to the substance dualist, mental processes occur in the mind, and not in the brain. (Many people like s.d. because it suggests we can live on after the death of the body.) Why then do damage to the brain or degenerative brain diseases affect our ability to think?
Property Dualism Property dualism denies that there are any non- physical substances. Instead, it says that some physical substances, in particular, brains, have mental properties in addition to their physical properties.
Pros of Property Dualism This can explain why brain damage, for instance, can change your mental states or your ability to have certain mental states.
Epiphenomenalism Property dualism is often combined with epiphenomenalism. Epiphenomenalism says that brain events can cause mental states, but mental states cannot cause physical events.
Pros of Epiphenomenalism The good thing about epiphenomenalism is that it doesn’t contradict physics. Since mental states can’t cause any physical events, it’s true (as physics says) that the motion of any particle is determined only by the physical forces exerted on it.
Cons of Epiphenomenalism The problem is that we have to deny two seemingly obvious facts about mental states: 1.Some mental states cause action. 2.Some mental states cause other mental states.
Abandon Dualism? Why not just abandon dualism? Well, many have done that. BUT, some philosophers think there are very good arguments for dualism. We will have several classes on them later. In general, they are arguments that conscious properties are not physical properties.
Substance Dualism Substance dualism says that there are two kinds of substances: physical substances with physical properties and mental substances with mental properties.
For Substance Dualism Arguments for substance dualism assume that physical things can’t have certain properties– creativity, originality, consciousness, etc. Since some things do have those properties, it follows that the things that do are not physical things.
Against Substance Dualism The primary reason for rejecting substance dualism is that it claims there are non-physical causes of events– but we have never found any! Second, it predicts that the mind should not be affected by damage to the brain, but this is obviously contradicted by experience.
Epiphenomenal Property Dualism Property dualism combined with epiphenomenalism can avoid these problems, but only at the cost of denying that mental states cause actions or other mental states.