The Mind/Brain Identity Theory:
A Critical Appraisal

4. Taming the Phenomenal Qualities Tiger

4.1 Evolution and the Paradox of Non-interactionism

Book cover: Cognitive Science: An Introduction to the Science of the Mind by Jose Luis Bermudez

In this final section of this essay, I want to discuss briefly the problem that phenomenal qualities pose for the identity theorists' programme and possible responses. I have argued that we must accept phenomenal qualities at their face value, at least until we are presented with a progressive research programme that allows us to ignore statements about them. An example of the type of successful eliminative programme I am referring to here is our set of current progressive theories on mental illness that now allows us to ignore talk of 'demon possession'. However, if in future we did encounter a research programme that allowed us to deny language about phenomenal qualities, we would be faced with an eliminative materialist view and not an identity theory proper.[15]

The first problem that I want to discuss is a paradox that I, for a while, had considered to be a serious objection to any kind of non-interactionism[16] that, on the one hand, takes seriously the semantic irreducibility of the postulates of theoretical physics to statements about phenomenal qualities and, on the other, takes seriously statements about phenomenal qualities. These include all types of psycho-physical parallelism and epiphenomenalism and those identity theories that are not inclined towards a phenomenalist interpretation of physics,[17] nor to a 'logical gap' theory of 'mental' terms.[18]

It was to be an objection that would make us seriously reconsider interactionism as a viable theory, in spite of the outstanding success of the non-interactionist programme. I include it here not only because I am less than fully confident that the objection can be answered adequately by the non-interactionist, but also because it is a suitable introduction to a consideration of the evidence for the identity theory vis-à-vis psycho-physical parallelism and epiphenomenalism.

The paradox is this. The non-interactionist claims that the whole of a person's behaviour, including his speech acts, has a sufficient causal explanation in terms of the entities and forces postulated by modern physics. Phenomenal qualities, he claims, play no part in such a causal account. Now, on this non-interactionist hypothesis, we could imagine a world (depending on the kind of non-interactionist hypothesis we are considering) that was identical to the actual world with the exception that in this possible world:

  1. there are no phenomenal events parallel to certain physical events (contra psycho-physical parallelism), or
  2. there are no phenomenal events that are epiphenomenal to certain physical events (contra epiphenomenalism), or
  3. phenomenal events are not identical with certain physical events (contra mind/brain identity theory).

According to the non-interactionist, in such a world we would do and say exactly the same things that we do and say now, including debating the mind-body problem.

However, this seems paradoxical and counterintuitive, for if there were no phenomenal qualities in this possible world, it is difficult to see how in this possible world we would have been lumbered with and debated about the relationship between mental events and physical events in the first instance. It seems that at least some of the speech acts that we commit while debating the mind-body problem would not have been committed unless there were some conscious mental events, such as conscious sensations of phenomenal qualities.

Statements about phenomenal qualities, then, seem to be a necessary inclusion in any adequate causal account of our speech acts. But if this is true, then the possible world that we have been imagining is not possible at all. That is to say, it is logically impossible, given our talk about phenomenal qualities, that the physical entities and forces currently postulated by physics could fully account for all of our speech acts. Therefore, it is logically impossible that the actual world be the way it is and non-interactionism be true.

How might a non-interactionist reply to such an intuitively convincing argument? The most fruitful reply, I think, is this. The non-interactionist begins by giving a physical account of the existence of a language of phenomenal qualities. (Even this sounds intuitively implausible on an interactionist view.) Such an account would refer to the considerable evolutionary advantage gained by a biological species whose members had the ability to, firstly, monitor their own internal physiological states (this is the basis of all homeostatic mechanisms) and, secondly, convey that information by vocalizing to other members of the same species. Other members of the group can respond appropriately when a member expresses a burning sensation or a feeling of fear, for example. Because the form of such intraspecific co-operation is highly adaptable to changing environmental circumstances, their capacity for co-operation would be greatly enhanced. Reproductive efficiency would be much higher compared with a reliance on the more evolutionary basic instinctual response.[19]

The next step in the argument is to introduce the adaptive advantage of learning. A species whose members can adapt their behaviour to changing environmental conditions has a distinct biological advantage. The relatively simple learning strategies, such as associative conditioning and operant conditioning, were, in the evolutionary development of the higher mammals, supplemented by the much more powerful strategy of postulating explanatory models of the environment and testing such models in novel situations. (This is akin to what psychologists have called 'insight learning'.)

Book cover: Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False by Thomas Nagel

Given sufficient biological sophistication and enough spare time, such organisms will not only develop models of their external environment, but also their internal environment. More importantly, however, models of the monitored states referred to in the phenomenal language will also arise. It is only a small step from here to the postulation of models showing the relationship between external and internal environments, and the monitored states referred to in the phenomenal language. Hence, we have the rough schemata of a physical explanation of the speech acts that we commit in debating the mind-body problem. Although, I must admit, I am not sure how far we can accept this explanation.

In spite of this intuitive qualm, there seems to me no doubt that what I will call the non-interactionist research programme has made outstanding empirical progress in explaining such things as human origins, mental illness, the effects of drugs on human personality, learning, and so on. I venture to suggest that this programme began with the inception of the mechanist school of biology in the eighteenth century and is now constituted by a number of specialist research programmes, including neurophysiology, neuropsychology, psychopharmacology, evolutionary biology and microbiology.

Research in these disciplines is governed by a methodological principle that states that whenever there is a theoretical problem, always avoid postulating the existence of non-physical entities or forces as a tentative solution. In Lakatosian terms, this principle constitutes the 'negative heuristic' of the programme. As a corollary, the 'hard core' of the programme comprises the postulate that the development and behaviour of all animals, including humans, is the result of the action of physical forces. The programme is non-interactionist in the sense that it bars the idea that such development and behaviour is ever the result of a causal interaction between physical and non-physical events.

The competing interactionist programme, however, which seems to me to be an extension of the vitalist school of biology, appears to have degenerated to the extent that it no longer constitutes a scientific research programme. Proponents of the interactionist programme have failed to develop detailed theories explaining how certain aspects of human development and behaviour are the result of the interaction between physical and non-physical entities or forces. Furthermore, they have failed to deduce and test predictions based on such models. All of my comments here are tentative because, as far as I am aware, no researcher has yet undertaken the task of writing a sorely needed Lakatosian historical account of the interactionist and non-interactionist research programmes.[20]

Where does this leave the identity theory? Even though some researchers working on the non-interactionist programme had pushed for an identity theory,[21] it is my impression that it did not constitute its hard core. If this is true, then the greatest problem for the identity theory is the supply of evidence that will sway us in its favour against its non-interactionist rivals; epiphenomenalism and psycho-physical parallelism.[22]

One way not to support the identity theory is through appealing to some principle of simplicity.[23] Although such a principle is necessitated by inductivist and conventionalist epistemologies, within a Lakatosian epistemology it is regarded as being a subjective criterion, and hence inconsistent with an objectivist methodology.[24] With this defence barred to him, the identity theorist can make one of two moves. He can either wait for predictive success from his own research program or claim that the identity in dispute is a brute fact about nature while at the same time pointing out the empirical bankruptcy of the interactionist's programme. I shall consider each of these approaches in turn.


  1. [15] This is not notwithstanding the fact that some commentators regard the Rorty-Feyerabend version of eliminative materialism to be a type of identity theory.
  2. [16] I mean by 'interactionism' here the view that some human behaviour is the result of the interaction between physical and non-physical forces. Conversely, 'non-interactionism' is the view that there are no such interactions.
  3. [17] An example of an identity theory that appears to me to be so inclined is H. Feigl's early version of his identity theory, or 'pan-quality-ism' as he called it. See his [1961]. Bertrand Russell's neutral monism may be another example. See his [1947: 860f].
  4. [18] Included here in the 'logical gap' versions are Smart and Armstrong's variants of the identity theory.
  5. [19] This account has the advantage over interactionist theories in that it derives as a novel fact the relative simplicity of the terms in the language of phenomenal qualities. (For the importance of the successful derivation of novel facts for the confirmation of an explanatory theory, see my Allan [2016b: §4.3]). For effective intraspecific co-operation, a highly complex phenomenal language reflecting the intricate complexity of the monitored brain states is not required. All that is evolutionarily necessary is that the language reflects the gross characteristics of brain states. So, a simple phenomenal language is what is to be expected on this theory. This simplicity is thus explained. At the same time, we would expect an evolutionary development towards greater complexity in the phenomenal language. That this has been the case, with the development of finer discriminations between mental states, is also a plus for this theory.
  6. [20] The memorable volume edited by Howson [1976] is the only collection of Lakatosian historical case studies of which I am aware.
  7. [21] For example, the naturalist, George John Romanes, (1885) Mind and Motion, in (1964) Body and Mind, ed. G. Vesey, London: 183 and quoted in Gregory [1984: 476]; and the psychologist, Place [1977].
  8. [22] For the purposes of this essay, I have not considered the more recent rival to the identity theory, functionalism.
  9. [23] J. J. C. Smart has pushed this defence for all it's worth. See his [1977: 84–7].
  10. [24] See my Allan [2016b: §4].

Copyright © 2016

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