Physicalism Feb. 12 14, 2014
Overview I Main claim Three kinds of physicalism The argument for physicalism Objections against physicalism Hempel s dilemma The knowledge argument Absent or inverted qualia
Review 3 main theories in the philosophy of mind literature: 1 Substance dualism Plato, Descartes: there are two kinds of substances: spiritual and physical (soul and body), and one can exist without the other. 2 Physicalism especially in the 20th century 3 Hylomorphism Aristotle, Middle Ages
Physicalism: Main Claim Main Claim of Physicalism: Everything is physical; everything can be exhaustively described and explained by physics. A form of monism (= there is one kind of entities) Everything = every feature of every individual; all the individual s behavior. All the entities that exist are physical entities the fundamental physical particles or materials that are described by physics. Exhaustively = the physical explanation leaves out nothing.
Implications of Physicalism If physicalism is true... Persons, if they exist, are either fundamental physical particles, or else collections of fundamental physical particles. Their behavior can be exhaustively described and explained by physics. A description of all positions and properties of all the fundamental physical particles that exist would provide a complete description of everything even though it never mentioned the di erence between living things and nonliving ones, or mental beings and nonmental ones. Thus, if there were a Super-physicist somewhere in the universe, who knew all but only the physical facts, he would know everything.
Three Kinds of Physicalism They di er in how they understand the relation of psychological descriptions and explanations to physical ones. 1 Eliminative physicalism: Psychological descriptions are all false. In reality, there are no mental states; psychological talk is just gibberish. Everyday talk about your feelings, desires is like talk about the Greek god Zeus when trying to predict the wheather. 2 Reductive physicalism: Some psychological descriptions are true: they directly correspond to physical descriptions. Mental states are really just physical states (e.g., states of the brain) Your beliefs and desires have physical features. 3 Non-reductive physicalism: Some psychological descriptions are true, but they do not correspond directly to physical descriptions. Mental states are part of an abstract way of describing physical states. Psychological descriptions do not have real explanatory value.
A few things to note: All physicalists agree that all things are physical (including non-reductive physicalists) This means that if you are a physicalist, there is no separate realm of the mental (this why it is a monist theory, as opposed to a dualism) Do you have souls, according to the physicalist? Well, it depends which kind of physicalist you ask. Eliminativist: No. Reductivist: Yes; it is physical, and you should talk about it in physical terms. Non-Reductivist: Yes; it is physical. You can talk about it in non-physical terms, but that will not add to the entities you have in physics.
Reduction vs. Non-Reduction Reduction: The ability of one theory to take over the descriptive and explanatory jobs of another theory. If T a takes over the descriptive and explanatory jobs of T b,thent b is reducible to T a. We use theories to describe and explain things to perform various descriptive and explanatory jobs. Sometimes in the course of scientific progress one theory takes over the descriptive and explanatory jobs of another theory. (E.g., Kepler s laws of planetary motion were reduced to Newtonian mechanics; physical optics was reduced to electromagnetic theory.)
Reduction vs. Non-Reduction Will ordinary psychological discourse be reduced to neuroscience? Reductive physicalism: YES. Caesar and the Rubicon Suppose we use psychological discourse to explain why Caesar crossed the Rubicon: Caesar crossed the Rubicon because he wanted to maintain political power, and believed marching on Rome the best means of maintaining it. According to the reductive physicalist: Wanting to maintain political power = Brain State A; Believing that marching on Rome is the best means of securing political power = Brain State B; Crossing the Rubicon = Muscular Contractions C. Thus, we can replace our explanation with this one: Caesar was in Brain States A and B, and whenever these brain states occur, they typically cause Muscular Contractions C.
Reduction vs. Non-Reduction Will ordinary psychological discourse be reduced to neuroscience? Nonreductive physicalism: NO. Psychological discourse satisfies special descriptive and explanatory interests. Therefore, physics, chemistry, neuroscience, and other branches of science cannot take over the descriptive and explanatory jobs we use psychological discourse to perform. But note: Nonreductive physicalism is still a form of physicalism. It does not say that psychological discourse describes something nonphysical. When we describe things psychologically, we are just describing them abstractly, using di erent terms. Analogy: if we describe juniors and seniors as upperclassmen, we are not describing any entities in addition to the juniors and seniors. We are simply describing the junior and seniors using a di erent term.
The Argument for Physicalism Physicalists agree and take it for granted that science is our best means to get to reality. The Argument for Physicalism: P In the past, whenever people have tried to explain things by appeal to nonphysical entities, those explanations failed, and by contrast a physical explanation succeeded. ) Therefore, whenever people try to explain things by appeal to nonphysical entities, those explanations will fail, and by contrast physical explanations will succeed.
The Argument for Physicalism The form of the argument: Inductive Justification for the premise: Examples from the history of science. Explaining magnetism non-physical spirits = electromagnetic force Explaining the movements of the planets by non-physical minds = gravitational force Explaining abnormal human behavior by non-physical demons = abnormalities of the brain In all of these cases, the failed nonphysical explanation was replaced by a successful physical one; thus, we have good reason to think that nonphysical explanations will always fail, and that physical explanations will always succeed.
Objections Against Physicalism 3 main objections: 1 Hempel s dilemma 2 The knowledge argument 3 The argument from absent or inverted qualia
Hempel s Dilemma Carl Gustav Hempel (1905 1997) Philosopher of science, logical empiricism Born in Germany; fled to the US, taught at Yale, Princeton Interested in philosophy of mathematics, nature of scientific explanation Best known for the Hempel s dilemma, and the Raven paradox
Hempel s Dilemma Hempel s Dilemma P 1 Physicalists must define physics either relative to a preliminary stage of its development or relative to the final, ideal stage of its development. P 2 If physicalists define physics relative to a preliminary stage of its development, then physicalism is false. P 3 If physicalists define physics relative to the final, ideal stage of its development, then physicalism is lacking in content (we do not even know what it is saying). ) Either physicalism is false, or else physicalism is lacking in content.
Hempel s Dilemma Form of the argument: Destructive dilemma (valid) Justification for the premises: P 1 : Sciences, including physics, develop in two stages: a preliminary stage when theories are advanced, falsified, and replaced by more accurate theories, and a final, ideal stage when the most accurate, unrevisable theory has been achieved. But if sciences progress in two stages, then physicalists must define physics relative to one stage or the other. Therefore, physicalists must define physics either relative to a preliminary stage of its development or relative to the final, ideal stage.
Hempel s Dilemma Justification for the premises: P 2 : If physicalists define physics relative to a preliminary stage of its development, then physicalism is the claim that everything can be exhaustively described and explained by that preliminary stage of physics. But not everything can be exhaustively described and explained by a preliminary stage of physics (this is why it is a preliminary stage it is partly false!). Therefore, physicalism is false.
Hempel s Dilemma Justification for the premises: P 3 : If physicalists define physics relative to the final, ideal stage of its development, then physicalism is the claim that everything can be exhaustively described and explained by the final, ideal stage of physics. But we do not know what the final, ideal stage of physics says (we are not there yet). Therefore, we do not know what physicalism says (the claim lacks content).
Hempel s Dilemma Hempel s Dilemma P 1 Physicalists must define physics either relative to a preliminary stage of its development or relative to the final, ideal stage of its development. P 2 If physicalists define physics relative to a preliminary stage of its development, then physicalism is false. P 3 If physicalists define physics relative to the final, ideal stage of its development, then physicalism is lacking in content (we do not even know what it is saying). ) Either physicalism is false, or else physicalism is lacking in content.
Hempel s Dilemma
The Knowledge Argument A further argument against physicalism. The Knowledge Argument P 1 If physicalism is true, then all facts are physical facts. P 2 But not all facts are physical facts. ) Therefore, physicalism is false. Form of the argument: Modus tollens (valid) Justification for the premises: P 1 : A fact is what corresponds to a proposition; if everything can be described by physics, that means that all facts are physical facts.
The Knowledge Argument Argument for P 2 : 2 i If it is possible to know all the physical facts without knowing all the facts, then not all facts are physical facts. 2 ii But is possible to know all the physical facts without knowing all the facts. P 2 Therefore, not all facts are physical facts.
The Knowledge Argument But why accept 2 ii? Conceivability-possibility principle: if I can imagine such a case (when someone knows all the physical facts, but not all the facts), then it is possible. Thought experiment for 2 ii : Mary s case Mary knows all the physical facts, yet she has never experienced color. She learns a new fact when she experiences color for the first time (e.g., sees a ripe tomato). But, of course, it is not possible for someone to learn what he or she already knows. Thus, in this case, we imagined a case when Mary knew all the physical facts, yet there was something she did not know.
The Knowledge Argument Summary Mary s example: we can imagine a case when someone knows all physical facts and yet does not know all the facts. = (conceivability-possibility principle) = It is possible that someone knows all the physical facts and yet does not know all the facts. = Not all facts are physical facts. = Therefore, physicalism is false.
Absent or Inverted Qualia Qualia = the subjective quality of experience; e.g., what it is like to see red. The Argument from Absent or Inverted Qualia P 1 If it is possible that your physical replica has absent or inverted qualia, then physicalism is false. P 2 But it is possible that your physical replica has absent or inverted qualia. ) Therefore, physicalism is false. Form of the argument: Modus ponens (valid)
Absent or Inverted Qualia Justification for P 1 : 1 i If physicalism is true, then either (a) qualia do not exist, or (b) qualia are physical things. 1 ii But qualia do exist (we know it from experience). 1 iii Therefore, if physicalism is true, qualia are physical things. [From 1 i,1 ii ] 1 iv If qualia are physical things, then your physical replica could not have absent or inverted qualia. [From the definition of physical replica ] 1 v Therefore, if physicalism is true, then your physical replica could not have absent or inverted qualia. [From 1 iii,1 iv ] P 1 If your physical replica could have absent or inverted qualia, then physicalism is false. [Contraposition from 1 v ]
Absent or Inverted Qualia Justification for P 2 : Conceivability-possibility principle; I can imagine such a situation, therefore, it is possible. Qualia Inverted qualia Absent qualia
Absent or Inverted Qualia Summary I can imagine that my physical replica has absent qualia Therefore, qualia cannot be physical But if physicalism is true, qualia are physical Therefore, physicalism is false.