In listening to the following philosophy of mind lecture by John Searle, and he mentions in passing the following argument against materialism (starting around 43 minutes into to the lecture):

  • Beliefs have the property of being either TRUE or FALSE.
  • Material brain states don't have that property, a neural configuration/brain state doesn't really change depending on whether it corresponds to a TRUE fact or a false fact.
  • Some mental states, namely beliefs, therefore have different properties than material brain states.
  • By Leibniz's law, since Beliefs and Mental states don't have the same properties, they can't be identical.

Searle then goes on to state that he isn't really convinced by the argument, but he doesn't elaborate any further.

How can one refute the argument? Using computer states or written language or painting or some other human artifact (i.e. some form of functionalism) as a counter example doesn't seem to work, because they ultimately derive their truth value (TRUE or FALSE) from the belief of whichever person created the artifact, so ultimately there has to be a purely mental phenomena at the source of the truth value of the physical representation.

What is wrong with this proof? How is it different from Kripke's modal logic argument and Chalmer's Zombie argument (I find it more convincing than those two, but it seems somehow related to them nonetheless)? Why does Searle not find it convincing?

  • 1
    How is this different from Searle's usual leap from does to is by appeal to ignorance, a.k.a. the rational psychologist's fallacy? philosophy.stackexchange.com/questions/31312/…
    – Conifold
    Feb 17, 2016 at 18:32
  • @Conifold In the meantime I have managed to get to lecture 8 in the course, and Searle is getting increasingly contradictory and inconsistent. He doesn't believe in Strong AI, and claims no conceivable future advances in computer science will ever achieve it, but seems to be a physicalist and claims that at some point in the future we will know enough about how the brain works to duplicate consciousness.I would just give up on the course all together, but I'm a sucker for freebies. Feb 17, 2016 at 21:13
  • I saw John Searle speak about 30 years ago. It is good to hear that he is still vexing and incomprehensible, dear old chap. I think that he does not find anything convincing except for his phrase "the bottom-up causal powers of the mind." Now he just needs to convince the rest of us.
    – user16869
    Feb 18, 2016 at 0:56
  • In the fourth bullet, don't you mean "Beliefs and Brain states," not "Mental" states? Feb 18, 2016 at 1:50
  • 2
    Truth is not something beliefs have, it is something we attribute to out of intuition, to simplify communication. I can believe either side of Russel's paradox, and that would be neither true nor false. Other paradoxes also poke holes in the notion of 'True'. So the argument is doomed from its first premise.
    – user9166
    Feb 18, 2016 at 22:06

6 Answers 6


The argument basically pre-supposes the conclusion in its second assumption. To make his argument work, his second assumption has to be rewordable to "material states are different than mental states," which is the conclusion. The only other possibility that I can think of for translating his second assumption is "two material brain states can be identical, but capture different facts," which is also a pre-suppositon of the conclusion.

I think the thing he's getting at is that we do not have a rule for separating the brain states of true beliefs from those of false beliefs. However, the fact that we do not have them does not state that they do not exist. You cannot claim they are not different merely because you do not have a process for distinguishing them.

His first assumption is tricky also. It sounds like a nice definition, and you are welcome to use it, but it is trivial to argue that beliefs are better modeled using modal logic because there are beliefs that are neither true nor false, such as the obvious paradox "I believe this sentence does not contain one of my beliefs."

  • The idea that indiscernibles are identical is a proposition of Leibniz
    – Joseph Weissman
    Feb 17, 2016 at 13:37
  • 1
    @JosephWeissman Good point. In that case, one is not presuming the existence of an external oracle which can observe the true state of the universe, which may discern the difference between brain states of beliefs (or may not) and thus discern materialism from dualism. We're only considering what we can discern. In that case, I would argue that we do not know whether brain states and mental states are indiscernable or not in the global sense, but are indiscernableto us, thus such a claim would not refute materialism, but would certainly defend the validity of dualism.
    – Cort Ammon
    Feb 17, 2016 at 15:34
  • 1
    And I just noticed an even more entertaining counterargument, again picking on his second assumption. His argument requires us to believe that the brain does not change state in the presence of a true fact or a false fact.
    – Cort Ammon
    Oct 8, 2018 at 23:58

Truth or falsehood of a belief is a relation between the belief, expressed as a proposition, and a fact from the physical world. To keep things simple I do not consider facts from the mental world.

The same holds true for those mental states which incorporate representation of facts. Either the model is a correct representation or it is a wrong representation. The model itself is a pattern of neural activities.

I even favor the view that the neurobiological substrate of beliefs are exactly such representational states.


The argument as outlined is not valid. Beliefs don't have truth properties, just as brain states don't.

The way one ascribes truth properties to them is different, though. So this might be a way to reconstruct the argument in a valid form. If mind and brain are identical, the outcome of all testing of them should lead to consistent answers. The METHOD one tests mind and brain are different -- so one could be in an indeterminate state in one test, while have established certaintly for the other. But if these are different manifestations of the same underlying reality -- that we discern these manifestations differently would not be a problem. It is only a problem for Identity Theory if the two answers are different ONCE THEY ARE SETTLED. This sort of test is how type-type identity theory was refuted, and forced Identity theory to become the nearly content free token-token version.

Richard Swinburne, in Mind, Brain, and Free Will, proposes a more powerful identity test. He notes there is a fundamental difference between mental and physical composites. Physical composites do not have essence -- the Ship of Theseus was just a convenient label, not a fundamental reality. But selves -- THEY have essence. Theseus is not just a label, he was an individual -- with actual continuity over time, despite changes in knowledge and cumulative history and physical components. If self has essence, and brain does not, they CANNOT be identical.

Swinburne's argument has the same form as what is presented here:

  • Selves are a mental phenomenon
  • Selves have the property of essence.
  • Material brains and brain states states don't have that property.
  • Some mental phenomena, selves, therefore have different properties than material brain states.
  • By Leibniz's law, since Selves and brain states don't have the same properties, they can't be identical.

The gap is between bullet points 2 and 3 in the question. Everyone gets diverted from the actuality that brain states are not about truth to the argument that beliefs have a superstitious power to be 'untrue'. This is like a "Virtus Dormitiva", and puts everyones' reason to sleep.

Brain states are reflections of perception, or memories of perception, or memories of memories, etc. In other words, brain states are ultimately about past inputs. We know that inputs can contain mistakes, misperceptions, but perceptions in themselves are not about truth or falsehood, they are simply experiences.

So what the brain was designed (or evolved) to focus on was to discern useful information, not to categorize truth and falsity. It is not a truth machine, it is an effect machine. Like a car, a car does not drive to true places and refuse to drive to false places: anywhere it can get to is its range. Asking whether the brain can entertain a false belief is like asking if a car can drive off a cliff: yes, but...

Another way to look at it is that logic is Boolean: true and false are the only possible states. Neurons on the other hand function in an analog manner. Unless we can re-cast logic to allow for a continuous variation between true and false, we can't really consider the brain as a machine for doing logic. We manage to 'emulate' propositional logic with our big brains, but other animals apparently cannot and even to us it is profoundly unnatural, erroneous and problematic.


I'm probably not getting this. Doesn't it hinge entirely on whether "true" and "false" are determined by a independent physical correlation?

In the case of "the room is dark" or "the room is light" the beliefs and responsive brain states can correlate T/F, even if negatively.

But beliefs need not correlate to external physical states, and brain states cannot correlate to independent states.

Beliefs can be overdetermined, underdetermined, or self-referencing, as in "I believe in God," which has nothing to do with any external, independent condition, yet can be "true." The external references can be physicalized, but the "self-references," that presumably indicate consciousness, cannot.

On the other hand, I do not see how a brain state can be "false" without reference to an independent system, in which case there is presumably no physical causation... apart from spooky actions, say.


In point 2, the claim is that a brain state doesn't change depending on whether it represents something TRUE or something FALSE. If beliefs are different, then, they would have to differ regarding whether they're TRUE or FALSE. Therefore, we could determine whether they're TRUE or FALSE by examining the belief by itself. (Otherwise, there would be no apparent change between a TRUE and FALSE belief, just like brain states, and point 3 fails, because there is no necessary difference between a belief and a brain state.)

Therefore, to determine truth, we can line up people with different beliefs on a subject, and examine their beliefs to find which is TRUE. Since this is evidently not the case, the three premises lead to something that is almost certainly false. One or more of them, therefore, is almost certainly false. Any argument that relies on the three of them is almost certainly fallacious.

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