Note: this is substanially drawn from an essay I wrote for a course on the philosophy of the social sciences last christmas.
The now sadly departed Donald Davidson was, in my humble opinion, a really bloody good philosopher (and not only in my opinion: Bernard Williams was, perhaps unsurprisingly given the similarity of their views on the embeddedness of human life in language and social practice, a great admirer according to Williams's Guardian obituary). Davidson worked on a number of areas in philosophy, but the most consistent theme through his work was a concern with the philosophy of language, of understanding how we communicate with and understand each other. This stemmed from a basically Quinean view of epistemology, holding that knowledge is bound together in a kind of web, and that this web is added to according to what it already contains. Originally developed in 'Two Dogmas of Empiricism', Quine's view turned on the idea that empirical evidence relating any theory never by itself refuted or proved the theory, because to make the empirical evidence relevant to a given theory itself required interpretation (this isn't quite the line he takes in 'Two Dogmas' but it is, I think, representative of his view more generally). For example, if I hold that all crows are black, and I see a creature which is like a crow in every respect but white, I have a number of options: I can believe that I am mistaken as to its likeness or hallucinating, I can hold that the creature is not a crow, and presumably, an indefinite number of increasingly bizarre things, or I can say that it refutes the claim that all crows are black. Which of these choices I make depends on which other claims in my belief-set I hold constant: faith in my perceptual equipment, most obviously.
Because such a theory makes all meaning contingent (or at least much more meaning that was conventionally philosophically assumed at the time of 'Two Dogmas'), it places a lot of weight on the contingent practice which gives meaning to things, language. Interpretation, in the broadest sense, of linguistic practice, then becomes the task of the philosopher. Davidson's work illustrates how what could be seen as a serious limitation on the work of philosophers should almost be seen as a liberation. He wrote on agency, events, and radical interpretation - what we have to do, what assumptions are necessary, to come to understand what someone whose language we have no understanding of - inventively and intriguingly. The part of his work I am most familiar with is his theory of anomalous monism, which claimed to reconcile three apparently contradictory intuitions about our mental lives, that they are not casually determined, that they interact casually with the physical world, and that all causes fall under general, strict deterministic laws. This triad appears incompatible because if, for example, my wanting an ice-cream causes me to get and eat an ice-cream, then it would seem to be the case that if causes fall under general, strict deterministic laws, then there must be such a law which explains my wanting an ice-cream, and my mental life must be determined.
Davidson’s solution to this problem, in his paper 'Mental Events', is to argue that any given mental event is identical with some physical event, and that this explains how the mental interacts causally with the physical world, but that there are no general and strict laws which link mental events qua mental events either to other mental events or to physical events. This means that the mental events do not themselves fall under any general and strict laws: the physical events which mental events are identical with fall under causal laws, yes, but the mental events do not. The argument turns on two points about linguistic practice, that the mental and the physical have distinct practices of property ascription, and that to fail to respect those practices of property ascription would be to fail to treat the mental qua mental, and that general and strict laws are themselves a form of linguistic practice.
He argues for this conclusion by showing that there are some properties which could not together be the subject of laws. The property of being ‘grue’, that is, blue until time t, and green after time t, would not go with the property of being an emerald, because physical objects like emeralds just do not suddenly change colour for no reason. The property of being an ‘emerire’, however, would go with the property of being ‘grue’, because it is the property of being an emerald until time t and a sapphire after time t. There could be law-like causal statements about ‘emerires’ and ‘grue’: there aren’t, as a matter of fact, because there are no ‘emerires’ and no things which are ‘grue’, but there could be. This makes it at least possible that properties might not be suited to be joined together in causal laws, because there.
What he further needs to show is that mental events and physical events fall into this class of things which are not made to be put together in strict, general laws. He does this through a discussion of length, the conclusion of which is that “just as we cannot intelligibly assign length to any object unless a comprehensive theory holds of objects of that sort, we cannot intelligibly attribute any propositional attitude to an agent except with the framework of a viable theory of his beliefs, desires, intentions and decisions”. If outside of this characteristically mental framework, attribution of propositional attitudes becomes unintelligible, then any attempt to attribute propositional attitudes on the basis of physical evidence, which would, of course, inevitably be in the framework associated with that vocabulary, would be unintelligible (and vice versa).
Davidson justifies this by asking us to consider what we would say if we were ever to come across a triad of objects across which length was not transitive, arguing that our whole theory of what length was, and what sort of objects we could apply it to, would in this case break down. This is because we do not have the conceptual tools to understand the idea that objects could have length without transitivity applying to them: the very idea of rigid objects only makes sense in terms of the idea of them having length and consequently being longer or shorter, and vice versa. Therefore, we can say that “the whole set of axioms, laws, or postulates for the measurement of length is partly constitutive of the idea of a system of macroscopic, rigid, physical objects”, that the two ideas are only intelligible in terms of each other. Davidson also makes the further claim that “the existence of law-like statements in physical science depends on the existence of constitutive … laws like those of the measurement of length” that we use to describe physical objects. Granted the first claim, it is unclear how this could not be true: if the very idea of “macroscopic, rigid, physical objects” is intelligible only with these “axioms, laws and postulates”, then the idea of laws governing such objects which do not depend equally on these must surely also be unintelligible at least, if not downright bizarre. Thus laws in physical science can only be suited to physical events and could not be used to describe mental events unless those mental events could be described in physical terms.
Not only does the mental not have these constitutive characteristics – it is clearly not a “system of macroscopic, rigid, physical objects” – it has another set of its own constitutive characteristics, because “we make sense of particular beliefs only as they cohere with other beliefs, with preferences, with intentions, hopes, fears, expectations and the rest”. The mental, because of this responsibility “to the background of reasons, beliefs and intentions of the individual” cannot be reduced to the physical: not only is it holistic and interdependent, subject to a degree of indeterminacy, but, crucially, since these could be, in part, resolved, by arbitrary choice of rules on which to attribute, it is also evolutionary. It grows and changes, and so, “we must stand prepared, as evidence accumulates, to adjust our theory in light of considerations of overall cogency”, with “the constitutive ideal of rationality” controlling this process.
Imagine someone who gave a false rationalization of their behaviour: if we at first accepted their explanation, what happens is that, because of new evidence about their motivations, we altered our assessment of their reasons, essentially eliminating some mental objects and replacing them with others. It can also be seen in the interactions of the mental with the physical, as the physical, by hypothesis, includes everything there is and could be, and so cannot interact with anything other than itself. Not only is this elimination and replacement elimination and replacement of objects in an indeterminate and holistic system, it is elimination and replacement which is itself indeterminate and holistic, and has no counterpart in physical theory.
Once we have measured something, its length does not change without some other physical object interacting with it, yet our attribution of a belief can change because we come to a new interpretation of an individual’s behaviour, without that implying that they have changed their mind. Mass and energy cannot be created or destroyed: these are fundamental laws of physical science, and yet, the mental apparently routinely accepts the destruction of its objects without dispersing its equivalents of mass and energy into its other contents. These features, the conservation of mass and energy, that length does not change without interactions with other physical objects, are crucial to the very idea of the physical – as we have seen, the physical is inconceivable without them (and they without it) – but the mental does not only not have them, it has their precise opposites and thus, speaking of the mental as physical is literally unintelligible.
This unintelligibility is created by two features of the mental, that it does not form a closed system in the same way that the physical does, and the constitutive role of rationality in governing that open system. This role is played for the closed physical system by theories like those of length, and the radical difference between the two constitutive theories, including the fact that the systems are respectively open and closed, is what means that there cannot be strict psycho-physical laws: to be indeterminate and holistic could be resolved by just deciding to do things in a particular way, but to be intelligible only under minimum constraints of rationality, and to have the ability to increase and reduce its size, cannot be arbitrarily settled in this way without changing the subject.
Further, given that the strict causal laws we do have are all couched in the vocabulary of the physical sciences, and the mental cannot be understood in terms of the vocabulary of the physical sciences, as we have just seen, it looks likely that the mental itself cannot have any strict deterministic laws. What is key, and makes it so implausible that there could be strict laws relating to the mental is again the fact that it does not constitute a closed system: to put the points expressed in the last paragraph in a different way, the possibility of causal laws vanishes once objects and events can appear and disappear under the influence of objects and events outside the system, because there is no possibility to exhaustively list the interactions of the various objects and events. This is because the interactions cannot be fixed, which is what causal laws are governing in the end, if the objects and events themselves cannot be fixed, which they cannot if they appear and disappear for because of interactions which are not themselves part of the system (interactions which could not themselves be specified under any causal laws appropriate for the domain in question anyway).
This has some implications for social scientists, because they can tend to see their project as attempting to articulate strict and general causal laws about human behaviour. Yet, if Davidson is correct, there are no strict and general causal laws about individual human behaviour, although there might be about social phenomena if they are not simply reducible to individual human acts. This bears on evolutionary psychology because it does seem to be attempting to, like psychology more generally, give strict and general causal laws about individual human behaviour. This is simply not possible if Davidson is right, which is of course not to say that evolutionary psychology is not useful or interesting, just that it’s not going to be giving us definitive answers to the questions it is currently trying to answer.
Update: It should of course also be noted that Davidson's argument leaves two avenues open. We could just stop talking about the mental at all: I understand that Churchland has proposed something like this, calling it 'eliminative materialism', and I think that Quine's own view about the philosophy of mind was something like this as well. If we're Quineans though, there might be a problem in that an epistemology which makes philosophy into a project of interpreting language needs to have room for interpretation. Stopping talking about the mental would seem to make it rather difficult to talk about interpretation, a definitively mental activity if there ever was one.