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Kripke Contra Materialism

Materialism, the belief that only physical or material things exist (denying anything spiritual or mental), has been a view in various philosophical circles for centuries if not millennia. Even today materialism exists, perhaps stronger than ever as a growing number of people turn their backs on the spiritual.

Interestingly enough, materialism is even evident in the philosophy of mind, a field one might think the materialists would shy away from. The materialist position is that the “mind” is an illusion created by the brain. One might, for example, compare the picture on a television screen. We see visions of people, things and hear voices… but these are merely projections of the television. They have no external reality and would cease to exist if the television ceased to exist. Just as the picture dies when the television dies, so too, materialists believe, the mind or soul dies along with the human body.

Materialists argue their point of view in the philosophy of mind under different headings, despite their many shared beliefs. One prominent theory is the identity theory of mind. Here we will present an overview of that theory, and the objections to it raised by anti-materialist philosopher Saul Kripke [1].

What Identity Theory Of Mind Is

The identity theory of mind goes by many names. Some of them are: type physicalism, type identity theory and mind-brain identity theory. For the sake of simplicity, I will be using the name “identity theory” to refer to this belief.

Identity theory posits that mental events are “type-identical” with the physical events in the brain with which they are associated. What is a “type”? Simply put, a term that summarizes a state of being. Let’s say that “pain” is a mental event type. Let us say that “C-fiber firings” are a physical event type. An identity theorist (materialist) would say that pain and C-fiber firings are one and the same (type identical).

There is also something called “token identity”, wherein each “token” is considered identical. The example given is the phrase “yellow is yellow is yellow is yellow”, where there are only two types of words (“yellow” and “is”) but there are seven tokens (four “yellow” and three “is” tokens). We will not concern ourselves with token identity theories.

Brief History

The idea of type-identity physicalism began in 1933, when psychologist E. G. Boring wrote The Physical Dimensions of Consciousness. In this book, he wrote, “To the author a perfect correlation is identity. Two events that always occur together at the same time in the same place, without any temporal or spatial differentiation at all, are not two events but the same event. The mind-body correlations as formulated at present, do not admit of spatial correlation, so they reduce to matters of simple correlation in time. The need for identification is no less urgent in this case.”

According to philosopher U. T. Place, philosophers and logicians had a difficult time accepting such vision a of the mind because they had not yet taken a substantial interest in questions of identity and referential identification in general. The prominent epistemology of the logical positivists at that time was phenomenalism, in the guise of the theory of sense-data. In fact, Boring himself subscribed to the phenomenalist creed, and attempted to reconcile it with an identity theory and this resulted in a reductio ad absurdum of the identity theory, since brain states would have turned out, on this analysis, to be identical to colors, shapes, tones and other sensory experiences.

Soon, logical behaviorism emerged as a serious contender to take the place of the Cartesian “ghost in the machine” and, although not lasting very long as a dominant position on the mind/body problem, its elimination of the whole realm of internal mental events was strongly influential in the formation and acceptance of the thesis of type identity.

There are subtle differences between the different formulations of the type-identity thesis of Place, Feigl and Smart, each of which were published in the late 1950s. All of the versions share the central idea that the mind is identical to something physical, our primary concern here.

U.T. Place’s notion of the relation of identity, formulated in the 1956 article “Is consciousness a brain process?”, was derived from Bertrand Russell’s distinction among several types of “is” statements: the “is” of identity, the “is” of equality and the “is” of composition. Place’s version of the relation of identity is more accurately described as a relation of composition. For Place, higher-level mental events are composed out of lower-level physical events and will eventually be analytically reduced to these. So, to the objection that “sensations” do not mean the same thing as “mental processes”, Place could simply reply with the example that “lightning” does not mean the same thing as “electrical discharge” since we determine that something is lightning by looking and seeing it, whereas we determine that something is an electrical discharge through experimentation and testing. Nevertheless, “lightning is an electrical discharge” is true since the one is composed of the other.

Herbert Feigl followed in 1957 and J. J. C. Smart came in 1959, both positing that identity was to be interpreted as the identity between the referents of two descriptions (senses) which referred to the same thing, as in “the morning star” and “the evening star” both referring to Venus. So to the objection about the lack of equality of meaning between “sensation” and “brain process”, their response was to invoke this Fregean distinction: “sensations” and “brain” processes do indeed mean different things but they refer to the same physical phenomenon. Moreover, “sensations are brain processes” is a contingent, not a necessary, identity.

Kripke’s Objections

Kripke in 1972, and David Chalmers later in 1996 argued that identity theorists failed because they were unable to connect phenomenal mental states (called “qualia”) to brain states. Qualia are the subjective qualities of a conscious experience, such as nausea, feeling pain or having emotions. Kripke would say that one has a sort of direct awareness of the nature of such qualitative mental states, and their nature is qualitative in a way that brain states are not.

Kripke argued that the only way to defend this identity is as an a posteriori necessary identity, but that such an identity — e.g., pain is C-fibers firing — could not be necessary, given the possibility of pain that has nothing to do with C-fibers firing. Kripke argues that heat is connected to molecular motion, but pain is not connected to C-fiber stimulation. Pain is strictly mental, while heat is objectively measurable. Pain could exist, according to Kripke, without the C-fiber firing.

“Materialism, in [the form of the identity thesis], often now gets involved in very intricate ways in questions about what is necessary or contingent in identity of properties — questions like that.” [Kripke: 23] (Kripke is concerned with identity, he only brings in materialism because they claim an identity bias.)

Kripke says that “some philosophers [notably Thomas Nagel and Donald Davidson] have accepted the identity of particular sensations with particular brain states while denying the possibility of identities between mental and physical types.” [Kripke: 144] “It is doubtful that such philosophers wish to call themselves ‘materialists’.” [Kripke: 144n]

Materialists may think of mental states as contingent, thus this “amounts to the view that the very pain I have now could have existed without being a mental state at all.” [Kripke: 147]

“Materialism, I think, must hold that a physical description of the world is a complete description of it, that any mental facts are ‘ontologically dependent’ on physical facts in the straightforward sense of following from them by necessity.” [Kripke: 155] Kripke says that intuition shows this is not the case.


Kripke’s objections rely on two primary assumptions: one, that we can have subjective mental experiences and two, that not all mental experiences have a parallel in a physical state. He notably relies on the sensation of pain, which he believes is strictly mental, as it could be felt different by each person, even if the same trigger were used to inflict pain.

How accurate Kripke is could be debated. A materialist may argue that pain clearly does have a connection to the physical, through nerves, and that the subjective experience could be boiled down to variations in the physical. In fact, as science continues to learn more about the human body’s neurochemistry, it seems likely that fewer and fewer things will be seen as strictly mental. Mental illnesses, for example, are often treated chemically, and the alteration of serotonin not only alters the brain but a person’s feelings and mental life. Surely, if this is possible, it may only be a matter of time before more connections are made between chemicals and the so-called subjective consciousness of a human being.


[1] While Kripke’s exact philosophy of mind stance is not clear to me, his anti-materialism is evident and was restated as recently as 2001: “I don’t believe in a naturalist world view. I don’t base my thinking on prejudices or a world view and do not believe in materialism.” He is also a devout Jew, even declining to use public transportation on Saturdays, though this may not indicate his views on the mind.


Kripke, Saul. Naming and Necessity. Harvard University Press, 1980.

Also try another article under Philosophical
or another one of the writings of Gavin.

4 Responses to “Kripke Contra Materialism”

  1. Chris Sarnowski Says:

    Why must Materialism hold that a physical description of the world is a complete description of it? A description of something is not the thing itself. That is, I think that there are no mental states (in the sense of some ghostly state that continues in the absence of physical existence), but not necessarily that we will ever be able to describe them completely in purely physical terms. But that’s because mental states (in the common sense) can be very complex, and just may not line up exactly with physical states.

    The whole notion of “qualia” is also controversial. We do not always have “a sort of direct awareness of the nature of such qualitative mental states”. I’ll at least say that there are cases where someone doesn’t know if they’re in pain or not, and I think that’s enough to call the notion of qualia into question. If M holds herself stiffly, say, and winces, but denies (sincerely) that she is in pain, I think it’s very plausible that an observer would determine she really is in pain, and further that M might agree later that she had been in pain at that time but didn’t realize it. This doesn’t directly support Materialism, but I think it’s a problem for the primacy of intuitions about qualia. We can be wrong about them, so they are not as privileged as they seem.

    My source for much of this crazy view is Daniel Dennett, “Consciousness Explained”, 1991. (I’d have to look up the publisher).

  2. Chris Sarnowski Says:

    I’ve gone and skimmed through Naming and Necessity again. If I understand Kripke right, he seems to be saying that we can imagine the following: there are two possible worlds, identical in every physical detail (and we don’t have to worry about how we describe the physical world – maybe we can’t describe it in any finite way), but in one world there is a particular bare sensation of pain and in the other world there is not.

    If that is what he is saying, I think he’s wrong. If it’s not what he’s saying, it’s not clear to me what a Materialist is obliged to explain.

  3. Jj Says:

    What exactly is so hard to get here? Simply put, it is not contradictory to imagine pain without c-fibers firing. Hence, they is a possible world where pain exists and c-fibers do not, which implies that they are not identical, because if they were identical, it would be contradictory to affirm the existence of a possible world W where both P exists and P does not exist (if P stands for pain).
    And how could we not be in pain if we imagine we are in pain? Someone else may of course affirm that I am in pain, and of course in the strict Wittgensteinian sense that is the only real meaning of pain, but again, it is possible to imagine being in pain and having no one believe me.

  4. TG Says:

    Pain without c-fibers firing is not *logically* contradictory, but that is not what (the version of) materialism (that I like) is claiming. Rather, it proposes, not as a “claim” but rather as a working scientific hypothesis, that pain can’t exist in our world without something like c-fibers firing (substitute some more up-to-date neurological description) for *physical* reasons. A simple analogy should make this clear: “the cow jumped over the moon” is not logically contradictory, but there are good physical reasons for why it can’t ever happen (the force the cow’s legs can generate is not sufficient to achieve escape velocity, etc.). So in this world, cows can’t jump over the moon, and in the same way, the hypothesis is that pain can’t exist without there being some corresponding physical state in the brain. Conversely whenever the appropriate brain state exists, the subject will experience pain. Exactly what that physical state might be is up to the science of neurology to establish at some future time.

    Now even if a conscious subject experiences pain if and only if the appropriate brain state exists, that doesn’t necessarily make them identical. But from a simple pragmatist perspective, what would be the “cash value” of positing that they were two different things? It would offer no explanatory advantage. It would be completely ad hoc. In that case, Occam’s Razor favors the assumption that they are indeed identical.

    Coming back to (the naive version of) Kripke’s argument (that is being considered here), to say “there is a possible world where pain exists and c-fibers do not” is misleading. What does follow is that the existence of such a world is not logically contradictory. But that doesn’t imply that such a world is actually possible. In order to establish that kind of possibility, one would need to specify a set of physical laws that explained how pain could be experienced by conscious beings, without it being identical to some physical state. Is it even “possible” to specify such a set of physical laws? I don’t know for certain, but I strongly doubt it. To highlight the difficulty, let’s go back to the jumping cow. I could posit a world where the gravitational force was much weaker, but would such a world support life as we know it? How much mass would the moon need to contain? I’m not a biologist or a physicist, but I think I’m posing a highly nontrivial problem. So even for this silly example, the task of specifying the set of physical laws required to make sense out of the statement “there is a possible world in which cows can jump over the moon” is in all probability beyond what we are capable of. And if that is the case, how much so for making sense out of “there is a possible world in which pain is not (identical to ) a physical process”? The statement “makes sense” only insofar as it’s consistent with the axioms of modal logic, or if you like, constitutes a well-formed-formula in that system, but I would insist on a lot more in order to have it “make sense” in a way that was relevant to the mind-body-problem. Lacking that, the conclusion that pain is not identical to some physical process simply doesn’t follow. Furthermore, even if a world in which they were not identical did exist, it still wouldn’t follow that they are not identical in *our* world.

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