Roadmap to Philosophy of Mind

Sandra LaFave

These notes have three parts:

  1. Substance Dualism: the mind-body problem begins.

  2. Materialism (aka Physicalism): the basic ontological view of most contemporary philosophers and psychologists. In this section, we look briefly at various forms of physicalism: Mind-Brain Identity theory, Eliminative Materialism, Soft Behaviorism, Logical Behaviorism, Functionalism, and Property Dualism.

  3. Metaphysical Pluralism: the rejection of both substance dualism and monist materialism; the metaphysical position underlying Logical Behaviorism, Property Dualism, and Functionalism.




I. Substance Dualism

According to Substance Dualism, Reality comprises two completely different kinds of substance: the material/physical (res extensa) and the non-material res cogitans. We'll refer to res cogitans as the “Mental” with a capital “M”. Res cogitans is special substance that can think.


Most contemporary philosophers and psychologists are materialists: they believe that consciousness events such as thinking and feeling are real, but that they are caused entirely in the body, especially the brain, as the body interacts with the world. In other words, most contemporary philosophers and psychologists believe in the "mental" (lower-case "m") but not the "Mental": they view the source of the mental as res extensa (body). They believe bodies can think. That's what Descartes couldn't imagine.


The following table shows the characteristics of the two kinds of substance in Cartesian substance dualism. According to Descartes, res extensa and res cogitans are the only kinds of substance, and anything that exists must be of one or the other type. Note that in substance dualism, the two categories actually have opposite and contradictory properties. This means that for Descartes, nothing can be both mental and physical in the same sense at the same time. Hence the two columns indicate strict alternatives: if something is in the res extensa column, it is automatically excluded from the res cogitans column and vice versa. This is the source of the notorious mind-body problem.



Descartes' View: Substance Dualism

(res extensa)
(res cogitans)
Physical OR Mental
Located in space OR Not located in space
Can be sensed OR Can't be sensed
Inert and passive OR Alive, active, creative
Has no intentionality or projects (doesn't want or do anything) OR The source of intentionality
Governed by laws of nature — determined OR Not governed by laws of nature — free
Divisible — made of smaller things (e.g., bodies are made of cells, which are made up of molecules, which are made up of atoms, etc.) OR Simple and indivisible
Can die or be destroyed if it breaks down into its component parts OR Cannot die or be destroyed because it can't be broken down
Measurable, quantifiable OR Not measurable or quantifiable
"Objective" OR "Subjective"
Public OR Private
The apparent self (the self from the "outside") OR The real self (self from the "inside")
"Lower" OR "Higher"


According to Descartes, the two different kinds of substance (in spite of having contradictory properties) somehow combine in human being. A person comprises:


1.       Res cogitans: thinking substance (mind or soul or consciousness)

2.       Res extensa: extended substance (body)


People obviously have mental (lower-case “m”) states; philosophers call such states "intentional" states. But what's distinctive about substance dualism is the notion that Mental (capital “M”) substance (res cogitans) is necessary for mental states. I.e., you can’t have mental states without res cogitans.


Some people think the following thought experiment clarifies the meaning of the mental. Suppose a “twin earth” that is physically exactly the same as earth, but in this twin earth, there are no minds or mental properties. What, if anything, would the twin earth lack? Your answer would presumably be the mental (the metaphysically subjective).


Substance dualists like Descartes and Christians add that the Mental is necessary condition of the mental.


According to substance dualism, then, both material and non-material substance are equally real, and are ontologically independent of each other (i.e., each can exist without the other).


Philosophers and psychologists disagree with substance dualism for the following reasons:


1. The mind-body problem: If sunstance dualism is correct, it seem impossible to explain exactly how the physical states of human bodies are related to the mental states. For example, how do the Mental and the physical interact, if the Mental has no physical properties? How can Mental events cause physical effects? Proposed solutions to the interaction problem seem especially lame (psycho-physical parallelism, occasionalism).


2. Gilbert Ryle’s objection in The Concept of Mind: Some phenomena seem very hard to classify, if we are stuck with the framework of Mental/mental OR physical, and we have to pick one. For example, disappointment seems both mental and physical. To insist on classifying disappointment as either mental or physical seems a category mistake.




II. Materialism (aka “Physicalism”)

Physicalism is the view that physical states of bodies are more fundamental than mental states of minds. The following are forms of physicalism.


1. J. J. C. Smart’s Mind-Brain Identity Theory


According to this view, mental events are real and are exactly the same things as brain events, which are material. Mental terms name realities, and those realities are brain events. So “pain” has exactly the same meaning as “C-fiber stimulation”, and the two terms are interchangeable.


Counterargument: To say that two terms mean exactly the same thing means that all predicates that apply to one apply equally to the other. For example, if “George W. Bush” has the same denotation as the phrase “43rd President”, then anything that is true of George W. Bush is also true of the 43rd President. If George W. Bush is six feet tall, then so is the 43rd President; if George W. Bush is married, then so is the 43rd President, and so on. In the same way, if “pain” and “C-fiber stimulation” meant exactly the same thing, then all the predicates that apply to one would apply to the other. However, some properties of pain seem not to apply to C-fiber stimulation. For example, pain is metaphysically subjective, whereas C-fiber stimulation is metaphysically objective; pain is private whereas C-fiber stimulation is public, etc. Thus, by modus tollens, “pain” and “C-fiber stimulation” cannot mean exactly the same thing.


Also, the mind-brain identity theory seems to arbitrarily exclude the possibility that consciousness could exist in creatures without brains e.g., robots or aliens. But many philosophers want to allow for the possibilility of multiple realizations of the mental in entities without brains, who don’t necessarily have C-fibers but might have pains. So mind-brain identity has been called a form of “neural chauvinism”.


2. Paul and Patricia Churchland’s Eliminative Materialism


According to Eliminative Materialism, neither mental states nor Mental states are real. The language of intentionality – the mental – is mere folk psychology. What people used to call pain is actually C-fiber stimulation (or whatever science finally decides it is). There really is no such thing as “pain”; only the C-fiber stimulation actually exists.


Counterarguments: (1) Consciousness seems real and undeniable from the perspective of the agent (from "inside"); (2) Human behavior can’t be explained at all without the language of intentionality.


3. Methodological (“Soft”) Behaviorism


Soft behaviorism makes no metaphysical claims about existence or non-existence of the Mental (res cogitans). According to methodological behaviorism, when we study behavior scientifically, we should not use the language of either the Mental or the mental (intentionality). For example, we should not say an animal prefers a certain kind of food F; rather, we should say the animal tends to move toward F when presented with food choices F and G.


Counterargument: Methodological behaviorism seems excessively reductionistic. It forces us to limit ourselves to descriptions of movements of bodies in space, but then we miss the biological and social levels of explanation entirely. We cannot understand what is happening on the human level by describing the bodily movements alone: for example, turning off the TV might be an act of kindness or an act of aggression, but the nature of the act would not be evident from the bodily movement alone, without reference to the perspectives of the agents involved.


Furthermore, soft behaviorism would make intentional causal accounts impossible. For example, you could never say “Amy was angry at Fred, so she turned off the TV”; i.e., Amy’s anger caused the TV to be turned off. Focusing on bodily motions alone misses that social level entirely.


Finally, it is often necessary to talk about the structure of bodies, in addition to their movements in space. In fact, scientific causal accounts do not all have the form of “First the cause (some motion), then the effect (some other motion)”. Many important causal explanations require continuous or emergent causality (e.g., the persistence of objects near the surface of the earth because of the continuous action of gravity; the continuous solidity of solid objects due to molecular lattice structures). Such structural properties are just as causally effective as kinetic ones, but their causality is continuous, not serial.


4. Logical Behaviorism (Ryle)


Behaviorism held sway in psychology until the 1960’s. The more extreme forms of behaviorism were philosophically on shaky ground from the start. For example, some behaviorists (e.g., B. F. Skinner) denied the existence of mental events altogether. Philosophers generally found that position a little extreme: it seems obvious that even if I can’t be sure anybody else has mental events, I do, and so I can’t deny that mental events exist. (Maybe I’m the only one who has them, but that’s a different problem. Maybe there’s no continuous me to have them, but that’s yet another problem.) Besides, the behaviorists often didn’t really eliminate intentional language at all; they simply substituted less intentional sounding words, e.g., “drive” for “instinct,” “food-seeking behavior” for “hunger,” “flight behavior” for “fear,” etc.


Gilbert Ryle (1900-1976), a British philosopher of the “ordinary language” school, tried to remedy these problems. Like the behaviorists, Ryle opposed the Cartesian view. But Ryle saw further that it was silly to claim that something had simply to be either “mental” on the one hand or “physical” on the other with no merging and no in-between. Ryle saw that if you limited yourself to the Cartesian categories, you ended up making category mistakes (like saying, if you’re a materialist, that intentions can’t exist because they’re “mental”; or if you’re a dualist, that intentional behavior can’t be observed because the intention is “mental”). The root problem is the Cartesian notion of the “mental” as totally opposed to the “physical.” Ryle came up with a new form of behaviorism, which he called logical or philosophical behaviorism. Logical behaviorism was opposed to methodological ("soft") behaviorism, which was behaviorist psychology’s policy never to use mental events in its “scientific” explanations of behavior.


Ryle did not try to deny the existence of mental events or intentionality; on the contrary, Ryle (following Brentano) said you must use intentional language to understand the behavior of people and higher animals. You have to talk as though mental events exist. Yet Ryle, like Skinner, tried to make mental events unnecessary in the scientific study of psychology. According to Ryle, any claim about “the mental” can be systematically reformulated as a set of “if … then” statements (conditionals), where both components (the antecedent and consequent) are observable behaviors. This way you can accept and use intentional language without utilizing any "unscientific" references to either the Mental or the mental. Everything that the science of psychology investigates exists publicly; there is one world, for epistemological purposes. But there are many ways to be in that world (metaphysical pluralism).


Logical behaviorism and non-intentional states (e.g., sensation)


Let’s look at how Ryle’s logical behaviorism would reformulate a statement about a non-intentional “mental” state such as sensation. Let’s consider the sensation of pain. According to logical behaviorism, the statement “John is in pain” MEANS the entire set of true conditional statements such as the following:




You ask John "Are you in pain?" John replies "Yes."
You measure John’s blood pressure You find it is elevated.
You stimulate John’s C fibers John winces, cries, says "OW!"
You see a bone sticking through John’s skin John winces, cries, says "OW!"
And so on ...

Logical behaviorism and Skinnerian behaviorism are similar in that both reject the Mental and the mental in science. The clever idea here is that if our list of conditionals is exhaustive enough, we’ll know exactly what it MEANS to say “John is in pain” without having to acknowledge the existence of any invisible mental events or feelings, since in all these restatements, the referents of both the “if” clause (the antecedent) and the “then” clause (the consequent) are public and observable.


Logical behaviorism and intentional states (e.g., belief)


Next let’s consider how Ryle would reformulate intentional statements such as “Jill believes it is going to rain”. For Ryle statements about belief are statements about dispositions to behave. Those dispositions to behave are just the true conditional statements such as the following (this is John Searle's example):




Jill leaves home Jill takes her umbrella.
Jill’s windows are open Jill closes the windows.
Jill’s garden tools are out Jill puts the tools in the shed.
Jill is wearing her good shoes Jill changes her shoes.
Jill drives her car Jill makes sure her windshield wipers are working.
And so on ...


Again, the clever idea here is that in all these restatements, the referents of both the “if” clause (the antecedent) and the “then” clause (the consequent) are public and observable, so we know what it MEANS for Jill to believe it’s going to rain without ever bringing in mysterious subjective private mental events called beliefs.


According to logical behaviorism, then, humans may have mental states but we never need to talk about them in science. (We do need them in life, however. The language of intentionality is indispensible to describe human action.) Logical behaviorists accept statements about the mental (statements of folk psychology) because those statements can be systematically translated into genuinely scientific statements. Talking about mental states is ultimately just talking about empirical correlations of observable behaviors, using the conditional forms described above. Thus, psychology (the science of behavior) consists of the discovery of “if-then” (conditional) statements of those correlations. The antecedent (“if” clause) describes one set of publicly-observable phenomena; the consequent (“then” clause) describes publicly-observable behavior. These correlations give completely adequate descriptions of the mental in terms of the physical. The task of the psychologist is systematic translation back and forth between the language of intentionality and the relevant conditional claims.


Counterarguments to logical behaviorism:

  1. You need to know everything about someone’s worldview and projects in order to know that person’s beliefs. In order to formulate the conditionals, you need complete information about everything that stands for everything else within a person’s world view – what someone sees things as. And there’s just too much of that stuff. For examples, see separate notes on Davidson.

  2. If all we mean by dispositions are these conditionals, and these conditionals make no claims about causality, then dispositions have no causal power. Logical behaviorism is nominalistic, in the medieval sense: there are only specific conditional linkages, and nothing more. Since the theory makes no causal claims, it is useless for science.


  3. Logical behaviorism ignores neurobiology.


  4. While logical behaviorism is philosophically an improvement over Skinnerian behaviorism, irreducibly mental events — mental events that can't be reformulated as behaviors — seem to exist. These are “raw feels” (aka qualia), such as the feeling of pain or the taste of pineapple, or what red looks like, or what it feels like to be a bat. It looks as though you could say everything possible about the physical, and your description would still leave something out, namely, the qualia. For example, see Frank Jackson’s "knowledge argument" for qualia or Thomas Nagel’s “What is it like to be a bat?” .

    Furthermore, as John Searle points out, you must invoke qualia to answer questions such as the following: what if someone were such a perfect actor that she could simulate pain behavior in absolutely all respects but felt nothing? Conversely, what if someone were such a perfect Spartan that he could feel terrible pain without displaying any behavioral signs? Logical behaviorism, which looks only at public behavior, would have to say the SuperActor was in pain and that SuperSpartan wasn’t, and both conclusions would be false. Thus, there’s more to the sensation of pain than a set of conditionals.

    The qualia problem also constitutes an objection to functionalism.



5. Functionalism


According to functionalism (Fodor, Putnam), “mental states are functional states that causally relate inner states with behavioral effects.” (Rahut, 153) The paradigm metaphor of functionalism is Xenon Pylyshyn’s “silicon-chip replacement” thought experiment.


“To begin the thought experiment, imagine that you are the subject of some mental event — perhaps you are experiencing an intense pain. Now imagine that one of your neurons is replaced by a silicon chip prosthesis that has the exact same input/output profile as the neuron it replaces. At the core of this thought experiment is the presumption that such a replacement would be unnoticeable to you or to anyone observing your behavior. Presumably, you would continue to experience pain even though the physical realization of those mental events includes a silicon chip where an organic neuron used to be. Now imagine that, one by one, the rest of your neurons are swapped for silicon prostheses. Presumably there would be no change in your mental life even though your brain, which was once made of lipid and protein neurons, is now entirely composed of silicon neuronoids. The physical feature of your brain that has remained constant and in virtue of which you instantiate the same mental properties, is not the stuff of which it is made, but instead the causal relations that each part of the brain bears to the other.” (Dictionary of Philosophy of Mind)


Functionalists, unlike logical behaviorists, assume the existence of "inner" states, but like logical behaviorists, they say those inner states must be ultimately hidden from scientific analysis. We can, however, analyze the processes by which inner states become public behaviors. That layer of analysis between inner states and behaviors is what functionalists call "the mental", and it is whatever does the job of "relating" inner states with observable events in the world: intermediaries such as human brains, alien brains, Turing machines, CPUs, immaterial souls, etc. all count as instantiators of "mental states" as long as these intermediaries do the job.


Most functionalists are metaphysical materialists, but functionalism is metaphysically neutral about the reality of the Mental (res cogitans).


Functionalists say a thing's mental states are exactly whatever is "in there" that does the function of transforming a thing's inner states into behavioral effects. Thus, functionalists say that if we don't know whether to say a thing has mental states or doesn't have mental states, we should look at how it behaves. Philosophers are particularly interested in "things" such as computers or robots or extraterrestrial beings. If the thing's behavior exhibits intentionality — if the thing's behavior is indistinguishable from the behavior of other things that exhibit intentionality — then we should assume something "in" the thing is doing the job of mediating between inner states and behaviors, i.e., we should assume the thing does have mental states.


Counterarguments to functionalism:


1. John Searle’s Chinese Room argument


“Imagine a native English speaker who knows no Chinese locked in a room full of boxes of Chinese symbols (a data base) together with a book of instructions for manipulating the symbols (the program). Imagine that people outside the room send in other Chinese symbols which, unknown to the person in the room, are questions in Chinese (the input). And imagine that by following the instructions in the program the man in the room is able to pass out Chinese symbols which are correct answers to the questions (the output). The program enables the person in the room to pass the Turing Test for understanding Chinese but he does not understand a word of Chinese. …The point of the argument is this: if the man in the room does not understand Chinese on the basis of implementing the appropriate program for understanding Chinese then neither does any other digital computer solely on that basis because no computer, qua computer, has anything the man does not have."

( Stanford Encyclopedia of Philosophy)

Searle's point is that something (e.g., a computer) could pass the Turing test and still not have mental states.


2. The distinctive feature of the mental is not a mechanism that does a job; rather, the distinctive feature of the mental is qualia.



6. Property Dualism


Property dualism is dualism — the view that the two metaphysical categories of dualism (mental and physical, subjective and objective) still that constitute all of empirical reality — but without the Mental. I.e., according to property dualism, human consciousness (the mental) is part of the physical world. Consciousness is a property of some objects in the physical world (e.g., animals and humans), but — at the same time — mental phenomena are essentially different from, and irreducible to, physical phenomena. No bodily terms completely explain the mental. We should therefore admit that two discourses are inevitable: one for the mental/subjective/intentional, and one for the objective/physical. There are the human sciences and the physical sciences, each with different and possibly contradictory claims (e.g., regarding free will). Davidson’s anomalous monism is a form of property dualism in this sense.



7. We’re not even close to an answer and maybe there never will be one (Chalmers, McGinn, Nagel).


Functionalists call these guys the “Mysterians”. According to these philosophers, the problem of consciousness is too hard, at least for now. Nagel says, for example, that we have no idea what it is like to be, say, a bat (i.e., what it’s like for a bat to be a bat), so we can’t possibly link bat consciousness to any physical event, because the experience of the bat is simply inaccessible. We can never get more than descriptions of the bat’s neural states; what bat experiences those neural states correlate with cannot be known or even imagined. So the experience side of the experience=brain event equation is currently (and possibly permanently) inaccessible.





III. Metaphysical Pluralism


All the forms of materialism/physicalism described here deny the existence of the Mental (res cogitans). By denying the existence of res cogitans, the forms of physicalism described here also reject Descartes' view that res cogitans and res extensa are mutually exclusive (since there's no res cogitans at all). The physicalisms described here also reject Descartes' characterization of res extensa as completely inert and passive; according to modern physicalism, brains (which are res extensa) think. Therefore, the terms "materialism" nor "idealism" can no longer mean what they meant in the substance dualist framework.

"Idealism" in the substance dualist framework had to mean that of the two metaphysical categories bequeathed to us by Descartes, only res cogitans (thinking, active, free, immaterial) exists and res extensa does not. There is currently no good reason to suppose idealism is true as thus defined.

"Materialism" in the substance dualist framework had to mean that of the two metaphysical categories bequeathed to us by Descartes, only res extensa (inert, passive, lifeless, etc.) really exists and res cogitans does not. Outside the substance dualism framework, "materialism" is still meaningful, and comes to mean a general commitment to empirical epistemological standards.

Ryle suggests we call the new "materialism" metaphysical pluralism. Pluralists reject the substance dualist characterization of all reality as either material or non-material (Mental); in other words, pluralism says there are many (and certainly more than two) conceivable ways to be. For Aristotle, real things are mostly individual things composed of matter and form. The form determines the “essence” of something — what it means to be that kind of thing. There are many ways to be, and so there are many forms.

Twentieth-century pluralists agree with Aristotle. They say there are many ways to be, and thus many metaphysical categories. Metaphysics has been trying to fit everything into one (or both) of dualism’s two categories. Yet what is is in lots of ways — not just one. We should stop thinking of reality as composed of a lot of changeless essences (represented by nouns), and start thinking of reality as a lot of ways of being put together or behaving (represented by adverbs). The way something is is the way it behaves or functions. And how something behaves or functions is public. So, the 20th-century pluralists say, there is only one knowable world, the sensible one; that's why they're physicalists. That is, there is one world for epistemological purposes. But there are many ways to be in that world. Furthermore, there is no problem in saying that that an individual exhibits more than one way of being. For example, one can be both a person and stylish. Furthermore, some aspects of the world simply cannot be reduced to the physical: for example, “aboutness” (physical things aren’t “about” anything, but mental/intentional phenomena are, in the sense that they have cognitive or sensory content).


Substance dualism has been particularly pernicious, according to twentieth-century pluralists. It has made human actions incomprehensible. According to all the forms of materialism/physicalism described in this essay, there are no ghostly Mental “events”; there are only publicly observable events, which can be in many ways — not just two ways (material and non-material). For example, disappointment is something (it’s real); but it’s not something either private and unobservable or public and overt. It’s usually both; but an even better way of describing it is to say it’s sui generis (it’s itself), a unique way of being in the world (being disappointed) that has obvious, recognizable, publicly observable characteristics. The same holds for other ways of human being: being thoughtful, shy, desirous, competent, stylish, embarrassed, jealous, willing, fearful, determined, etc. Intentional predicates refer to ways of human being or doing in the (one) world — what Wittgenstein would call “forms of life”.




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