Greg Detre
@12 on Friday, October 20, 2000
Prof. Snowdon
The Identity theory of mind can be understood simply as the claim that every mental property is identical with some physical property, i.e. every mental state or process is one and the same as a physical state or process. Thus, the mind-body problem as considered by dualists collapses into monism. To the best of contemporary scientific understanding, these physical states and processes are localised as neurochemical activity in the brain.
A dualist�s initial reaction to such a theory might be one of stupefaction: how can the plainly non-physical, private phenomenology of the mental be in any way akin to the physically deterministic, objective neural activity of the squishy brain? It is important to note that Identity theorists are not saying that mind and brain per se are identical or interchangeable terms, but rather that mental experiences just are brain processes (an even stronger claim than being merely correlated with each other).
Smart played a role in the group which first outlined psychophysical Identity theory in the 1950s, along with Feigl and Place. He distinguishes himself from the central state materialists, for whom �mental states are actual brain states�, as well as dualists, �nomological danglers� and �excrescences on the fair face of science�. Rather, as Lewis and others after him, he sees himself as a physicalist, looking for explanation in terms of physical laws, though which may admit non-material entities. He takes pains to specify that his brand of physicalism is ontological, rather than translational (i.e. word-for-word).
This original formulation of Identity theory holds that mental and brain processes are extensionally identical, but intensionally different in terms of how we perceive, identify and refor to them. Smart draws attention to the example often used to distinguish meaning and reference of Hesperus vs Phosphorus, or the Morning Star and Evening Star. Only relatively recently has it become apparent that Hesperus and Phosphorus are one and the same astronomical object, simply seen at different times of the day and in different parts of the sky. Thus our reference, (i.e. the names we use � intensional) draw a false distinction between two ways of seeing the same object (extensional). The mind and brain are to be seen in a similar way.
Lewis (1966) elaborates an argument for the Identity theory by analysing what we mean by �experience�. He takes as his crucial premise that �the definitive characteristic of an experience � is its causal role [in our actions]�. He takes as his second major presmise the physicalist[1] one that our causal role is in fact played by physical (i.e. neural) states/processes. Therefore, since the definitive characteristic of experience is played by physical states/processes, experience must be physical. If one accepts the two premises, one must accept the conclusion. But those two premises leave plenty of room for contention.
Lewis is really making use of Leibniz�s Law of Identity, which holds that two objects are identical if they share exactly the same properties. If this cannot be said of mind and brain, then the proponents of the Identity theory are committing a �category error�. Lewis� argument pivots around the definitive characteristic of experience being solely its causal role. But what if we can point to other characteristics of the mental, without which an experience wouldn�t be an experience?
For instance, though the brain is extended (in the philosophical sense of being physically located, and taking up space), whereas mind appears not to be. It seems somewhat nonsensical to say that there is a thought in the car park, say � rather, thoughts can be localised in terms of the self to whom they occurred. We have to be careful at this point not to allow the correct use of language to too strongly colour our analysis. Copernicus� statement that the earth moves around the sun was described scornfully as an �abuse of language�, because �movement� is by definition relative to the earth, so to speak of movement of the earth is to play games with words. Defining reality by reference to how we describe it linguistically, if that is indeed what we are doing, would be a mistake. But perhaps we can move the debate to firmer ground by considering another property of the mental that seems fundamentally at odds with the physical, its subjectiveness.
Nagel gives us powerful ammunition to use against those who seek to downplay the importance of phenomenological subjectivity in the mental, as Lewis does by defining experiences in terms of their causal role alone. In �What is it like to be a bat?�, he attacks the Identity theorists� methodology, of regarding the mind-body problem as simply a modern example of problems like the water-H2O problem, which have fallen to intertheoretic reduction and the scientific method. Nagel is most concerned with the Identity theorists� treatment (or failure to treat) what he calls the �subjective character of experience�. He is referring to the way that everyone�s experiences are subjective to them (as best we can tell, given our own subjective view on the matter). We cannot understand what it is like to be a bat � only a bat can. If we try and imagine, then at best we can conceive what it would be like for us to be a bat. It is this privacy of the mental which makes a reconciliation between an objective, scientific, physicalist understanding and our individual, incommunicably subjective perspectives so problematic, as Nagel rightly argues.
However, I see the shortcomings of the Identity theories more particularly in terms of the peculiar, non-physical, vivid, indescribable, irreducible quality and sensation to the (human) conscious experiencer of experience which is experience. To ignore this aspect of the mental, call it the subjective character of experience, �qualia� or phenomenology, is to ignore the mental. The problems facing natural philosophers about soundwaves, heat, colour and the like all concern separate sensory modalities whose physical principles and physiology we now understand. But we don�t understand any better why a noise sounds the way it does or why a fire feels hot. To say that we undestand them by virtue of the reductionist�s scalpel is to answer �How can we understand and predict this physical phenomenon?�, but misses the difficult half of the original question, �And why does it feel like this to me?�.
We can now challenge Lewis� premise that the defining characteristic of experience is its causal role. Whether we choose to posit the subjective phenomenological quality of experience as its defining characteristic as well as, or in place of its causal role is a separate question. A full account of experience would, I think, seem to need both these characteristics: a subjective feeling of what that experience is like, and causal interaction that allows experiences and thoughts (in the same way that folk psychology attributes our actions to intentions, beliefs and desires) to give rise to actions and other experiences.
If we were to try and rid experience of both its causal role and its phenomenological quality, we would be left close to behaviourism, where our actions can be seen as determined in a hugely complex version of the stimulus-response paradigm, seeing humans much like zombies (behaviourally and constitutionally identical to humans, but lacking consciousness). Logical behaviourism places a veneer over classical behaviourism, by arguing that we can impose intentions, desires and beliefs onto others� actions as a means of making sense of others in an internal model, but in fact these actions are still determined purely by (an albeit complex) behaviourist model.
First, I want to discuss what the implications of characterising experience solely by its subjective quality, and leaving its causal role aside.
This is the position we are left in if we deny Lewis� first premise, but accept his second: that causality in our universe is determined by laws of physics (including those beyond contemporary understanding of them). We will try at this stage to leave deterministic physics its jurisdiction over the workings of our universe. If this is the case, then the neural mechanism is open to discovery by the scientific method, and explicable and predictable according to universal physical laws. Given that we are taking Identity theory to mean the neurochemical activity of the brain by �physical states and processes�, Identity theory appears to be denying downward causation from mind to brain. This is the critical issue that Davidson seeks to address with anomalous monism.
Davidson�s anomalous monism is a token Identity theory. By that, we mean that he is identifying particular brain states/processes with particular mental states/processes. Crucially, he does not seek to identify types of processes (e.g. pain, or similar sensations) with each other. He takes as premises the nomological character of causality (i.e. physical laws), the anomalism of the mental (freedom from such deterministic laws) and causal interaction between the mental and physical. Causal relations occur under neural descriptions, but not under psychological descriptions because of the indeterminacy of translation and interpretation that occurs between the neural and psychological descriptions.
Davidson argues strongly that despite the apparent conflicts between his premises, he is able to demonstrate a reconciliatory explanation. However, Kim and others doubt the causal efficacy of the mental in such a picture. For them, anomalous monism falls prey to the criticism of epiphenomenalism. We have said that Lewis� Identity theory leaves little room in its explanation of the mental for phenomenology, i.e. non-physical, private events and states. Here, we have taken things to the opposite extremes, allowing such an added dimension to the mental, but denying it the causal role that we must as physicalists (since the brain obeys deterministic rules, how could our thoughts be anything but spectators in our actions). Here, our phenomenological experience is delegated to �epiphenomenon�, an evolutionarily non-adaptive side-effect, perhaps of language or high-level cognitive processes working within a rich internal representation of the world. In a weird kind of paradox, the homonculus Dennett tries to exorcise from his controlling role in a� Cartesian theatre of the mind is reinstated, but more as the audience than as the playwright.
Identity theory avoids the problem of interaction between mind and body by regarding them as simply interactions between subsets of material states. To an Identity theorist, the secrets of the mind will fall to neuroscience in the same way that the theory of electricity reveals the secrets of lightning. However, how this will happen is left mysterious.
Nagel identifies parallels between pre-scientific notions of his �a posteriori necessary truths� like water, lightning, sound and heat, and current philosophy of mind. Such problems suffer from what he expressively terms an �explanatory gap�, characterised by an ineliminable vagueness in our discussions, because we have an inadequate conceptual toolbox for the problem. Understanding sound in terms of soundwaves, or mind in terms of brain, involves bridging two terminologies and levels of explanation which cannot initially be explained or even imagined in terms of the other. Indeed, glossing over these questions in the same fashion with mind is to gloss over the grand-daddy question underlying them all. For all of these intertheoretic reductions are, at their root, problems of mind, not matter. Understanding the physics of a soundwave tells us nothing about the noise we hear. We cannot attempt the same reductionist approach in philosophy of mind that worked on these problems, because reductionism fails to explain (or often even recognise) phenomenology. Phenomenology[2] is the great problem in philosophy of mind.
We know that mind and body appear inextricably related causally, but it seems impossible to imagine how their seemingly irreconcilably different properties can be identified with each other. Perhaps speculatively though, if we come back to the crucial physicalist caveat, that the laws of our universe are certainly more complicated than our current understanding of them, then there may be room for some far-fetched seeming reconciliations of the subjective quality and the causal role of experience that we discarded as being in violation of deterministic physical laws. This is the approach that Nagel tentatively points to (as in �Panpsychism�) and Penrose embraces through the sub-atomic haziness of quantum mechanics. Such ideas are early attempts at bridging the explanatory gap separating mind and body from both sides at once.
[1] In this essay, I will use the term physicalism as the view that all factual knowledge can be stated in terms of physical objects and laws governing their interactions. This is intended to be slightly looser than the way the term �materialism� is sometimes used, and so avoid any confusion that may result through their interchangeable use.
[2] I have avoided the term, �consciousness�, because it is overly associated with human, linguistic awareness of higher thought processes. This way, I hope to open up the idea of phenomenology to easily accommodate a similar consideration of the mental in animals.