Putnam presents a version of functionalism – a position in the philosophy of mind which says that mental states can be deﬁned in terms of their causal roles – as an empirical hypothesis worthy of investigation, especially in light of what he sees as the problems facing the identity theory of mind and behaviorism. Central to Putnam’s conception are the notions of the Turing Machine and of
a Probabilistic Automaton. A Turing Machine is a hypothetical device proposed by Alan Turing which computes various tasks in a deterministic fashion, given certain instructions and given a machine table which speciﬁes how various states of the machine relate to one another and to inputs. (Readers are encouraged to investigate the machine more fully if they want the technical details. The points to understand are that the machine computes deterministically, and that it has its behavior entirely produced by input and states which ’react’ to the input in a speciﬁc fashion, producing computations and transitioning to other states automatically). A Probabilistic Automaton, meanwhile, is very similar to a Turing Machine, except that the transitions between states produced by input are determined
probabilistically rather than with certainty.
Putnam ﬁrst addresses whether the question “Is Pain a brain state?” is meaningful at all. Putnam in quick succession defuses the objections to the thesis that the question has merit. One such objection is that pain cannot be a brain state because we can know we are in pain and simultaneously not know that we are in brain state ’S’. But this objection also applies to us knowing that there is heat in the oven: we can know that the oven is hot without knowing
that its mean molecular kinetic energy is high, despite the fact that heat just is mean molecular kinetic energy. He further argues that the notion of Pain being a brain state is at least intelligible, if not necessarily true, just as other, successful empirical reductions (e.g., water being reduced to H20) have been intelligible.
Two objections remain. The ﬁrst states that the proposed reduction of Pain (and other mental states) to a brain state cannot be successfully engaged unless both things in the reduction are associated with a spatio-temporal area, and the spatio-temporal area is one and the same for both things. Putnam thinks this is wrongheaded and gives a counterexample: the reﬂected image oﬀ of a
mirror is merely reﬂected light, despite the fact that the image can at times appear behind the mirror. That is to say, empirical reduction is successful (the image is merely reﬂected light) despite the two things not sharing a spatio-temporal area.
The last objection states that, at best, brain states can be correlated with mental states, but never said to be equivalent to them. The predictions yielded from saying that the brain state and the mental event are correlated are equivalent to those which are yielded when we say that the state is the mental event, and there is thus no principled way of preferring the one over the other. Putnam agrees with this in a sense, but says that the two diﬀerent views enable/prevent certain empirical questions from being asked. So there is a meaningful diﬀerence between the two stances. For example, if we assume that identity obtains, the question “What makes the pain accompany the brain state?” is rendered meaningless.
With objections to the very idea of reduction of mental to physical dealt with, Putnam presents his model of functionalism. The model deploys the concepts detailed above: the Turing Machine and the Probabilistic Automaton. The idea is that mental states are functional roles within a system, where a system is (in the case of humans) a Turing Machine with a probabilistic transfer between
various states. Putnam denotes the complete functional proﬁle of a system – a complete account of all states and their probabilistic relations with one another and with sensory input – as the description of the system. Further, the behavior of the system is understandable without knowing how the system is realized. In other words, the mind can be understood perfectly well without understanding the particulars of the physical-chemical brain states which realize the mind’s functions.
Putnam admits that his model is vague on the details: the model says nothing, in fact, about how the functional states are to be deﬁned (e.g., what does it take for an organism to be ’in pain’?), nor does it say how exactly the functional states relate to stimuli. Nonetheless, Putnam thinks his model is advantageous over the identity theory of mind because it presents researchers with an em-
pirical research program which is less vague, and easier to carry out, than any research program under the auspices of the identity theory. Putnam then espouses the virtue of his functionalism over the identity theory in more depth, but also its virtues over behaviorism.
Putnam thinks his functionalism presents a more tractable research agenda because in the case of the identity theory, there must be a singular physical-chemical structure which is, say, pain. If identity theory is true, then researchers will have to ﬁnd the exact same physical-chemical structure in all the creatures which feel pain, and not ﬁnd it in creatures which do not feel pain. Putnam admits that this is possible, but thinks that identifying a functional proﬁle which is a commonality to all the organisms is more reasonable than trying to identify the exact same physical structure in all pain-feeling organisms.
Putnam extends his previous point to apply to the identity theory’s application to all mental states (and not just pain). Indeed, identity theorists have argued that all mental states are merely brain states. Putnam thinks this is almost certainly false, because in order for all mental states to be brain states, the entire physical-chemical structure of all organisms who experience such mental states will have to be the same. And Putnam thinks that this is most unreasonable: if even a single mental state is found to be experienced in another creature, and that creature has a diﬀerent physical correlate of the mental state than any other creature, then the identity theory is false.
Putnam then advances reasons for his theory. The ﬁrst is that we identity mental states in creatures in light of their behavior, and the commonality in behavior across organisms suggests a similar functional organization, but not a similar physical-chemical organization. This fact is Prima facie evidence for functionalism. Further, we tend to identity mental states in organisms based upon the behaviors they produce and the transitions into other states which they presage. So, we identity ’thirstiness’ partly by the fact that it tends to produce a certain behavior, which then tends to transition the system to another state, namely, ’not needing liquid anymore.’ And this fact about how we delimit mental states from one another suggests the appropriateness of a functional approach to such states.
Putnam then compares the functional approach to behaviorism, another
theory of identifying mental states. In the case of behaviorism, the mental states are deﬁned as a behavior, or disposition to behave, on the part of an organism. Putnam gives a reason for supposing behaviorism is not particularly advantageous: despite the fact that we identify mental states by using behavior, this fact does nothing at all to suggest that the mental state actually is the behavior. At the time the article was written, behaviorism was facing serious conceptual diﬃculties (from which it would never recover), and Putnam (as he recognizes) is thus able to recite these diﬃculties. One is that it seems impossible to identity a behavioral disposition without referencing the concept one is attempting to deﬁne. So when the disposition of pain is deﬁned, one must say something to the eﬀect of ’pain is a disposition of X to behave as if X were in pain.’ In contrast, a functionalist can simply identity a functional state which pain can then be equated to. Further, there can be animals (or persons, if you wish!) who show no diﬀerence in behavior and yet are experiencing diﬀerent mental states. A person X might be in pain and yet be suppressing their pain behavior, whereas a person Y may be in excruciating pain and yet have their motor nerves cut so that they cannot engage in pain behavior. And so pain is not the behavior in either case; it is something else.
Putnam concludes by reiterating methodological reasons for accepting a functional approach to mental states: One, the functional approach precludes certain questions from being asked (e.g., “Why does pain always accompany functional state S?”); two, the functional approach actually explains the behavior in question, rather than identifying mere correlations, and third, laws of psychology can be developed once an organism’s description (in Putnam’s sense) is known and a mental state is identiﬁed with a functional state.
Primary Argument: Functionalism is preferable to the identity theory and behaviorism as a theory of mental states
1. Either functionalism, the identity theory, or behaviorism is the preferable theory of mental states.*
2. The identity theory is not a preferable theory of mental states.
S1. For the identity theory to be viable, a mental state needs to have
the exact same physical correlate in all organisms which experience that mental state.
S2. Very probably, organisms experience the same mental state with
diﬀerent physical correlates of the same state.
S3. Therefore, the identity theory is probably not viable. [S1,S2]
3. Behaviorism is not a preferable theory of mental states.
S1. For behaviorism to be viable, one must be able to deﬁne mental
state dispositions without referencing the mental state itself, and thus
S2. It is not possible to deﬁne a mental state disposition without
referencing the mental state in question, and thus avoid circularity.
S3. Therefore, behaviorism is not viable. [S1,S2]
4. Therefore, functionalism is the preferable theory of mental states. [1,2]
5. There exist reasons for adopting functionalism, independent of the problems of the identity theory and behaviorism.
S1. A theory of mental states which enables a robust research pro-
gram is to be preferred.*
S2. Functionalism provides a reasonable commonality to identify
among organisms – functional states.
S3. Functionalism successfully prevents a number of questions from
being asked (questions which can waste researchers time).
S4. Functionalism – through its description of organisms’ functional
proﬁles plus identiﬁcations of mental states with functional states – promises to provide laws of psychology.
S5. Therefore, functionalism enables the most viable research pro-
S6. Therefore, functionalism is preferrable. [S5,S1]
6. Therefore, functionalism is preferable over the identity theory and over
behaviorism as a theory of mental states, and there are reasons to adopt
it independent of the other theories’ diﬃculties. [5,6]
*Asterisks denote enthymemes, or ‘suppressed premises.’ All these are are assumptions which must be made in order to make the explicitly stated argument work.