He rejects that there are type identities between the mental and the physical. That is, no mental property or type of event is identical to any physical property or type of event. (In the way that Smart proposed that pain was identical to C-fiber firing.)
Some might doubt that there are any such identities because Who has been able to say for sure what they are? But Davidson’s grounds for resisting this are more systematic and principled. As we’ll discuss below, he doesn’t think that there can even be any laws connecting mental types to physical events. But there are laws connecting phyical events like C-fiber firings to other physical events. If the property of having your C-fibers fire were identical to the property of being in pain, then it seems Davidson would have to allow laws connecting being in pain to the same physical effects that C-fiber firing is connected to. After all, they’re the same property.
However, Davidson does allow that there can be token identities between specific token mental events and token physical events. My running pain on Monday may be identical to my C-fibers firing in such-and-such ways at those particular moments. The Martian’s pain on Tuesday may be identical to different kinds of physical events in its body. Maybe there’s no identity between all cases of pain and any particular physical property. But it’s still plausible that each token pain event was just a matter of some particular physical goings-on (different in the different cases).
Davidson’s willingness to accept this is connected to his willingness to say that the token event of my running on Monday is identical to my wearing down my shoes then, and to my waking you up then. As we said, other philosophers wouldn’t count these events as identical but rather as closely connected. What you choose to say here depends on other metaphysical views you have and arguments you accept.
The next element in Davidson’s picture is his acceptance of the thesis that singular causation, between specific token events, always needs to be underwritten by a general law. Additionally, Davidson thinks that these laws have to be strict (exceptionless).
However, if what is doing the causing is a token mental event that is identical to some token physical event, the causal law that authorizes that causing to take place might be a strict law that connects the event’s physical type/properties to some physical type of effect, rather than a law that connects its mental type/properties to that effect. This is good, because on Davidson’s view there can’t be any strict laws connecting mental types to physical types. We’ll discuss why he thinks this in a moment.
Here’s the example I gave in class to help understand Davidson’s picture.
Suppose we’re playing a fantasy role-playing game with strange rules. Characters in the game can belong to various Species, like Elf, Human, Orc, Dwarf, Angel, and so on. They can also have various Vocations, like Wizards, Warrior Monks, Knights, Thiefs, Shamans, and so on. (Often these games use terms like “Race” and “Class” instead of “Species” and “Vocation,” but that vocabulary can reinforce unfortunate prejudices. I’m trying to improve that a little.)
The rules for our game will need to be pretty dumb, in order to make the analogy to our philosophical discussion work. But play along.
Some characters might not have a Vocation; for example, maybe some Humans don’t have any Vocation, and maybe Angels never have any Vocation. There might be some strict correlations, for example, that only Orcs can be Shamans, but in general Vocations include characters of various Species. For example, both Humans and Elves can be Wizards. Characters of any Species (except Angles) can be Thieves. And so on.
One thing this example illustrates already is that we don’t have type identities between Vocations and Species. You can’t say that Wizards = Humans, because Elves can also be Wizards. You can’t say that Wizard = Human-or-Elf, either, because some Humans and some Elves aren’t Wizards (they might belong to a different Vocation, or to no Vocation). And so on. Nonetheless, every particular member of a Vocation belongs to some Species or other. This particular Wizard may be a Human named Caleb. The next Wizard may be a Elf named Ludinus. And so on. But not every member of a Species belongs to any Vocation. So, going back to mental and physical, the Vocations would correspond to mental types (every token mental event is identical to some physical event, but they may be identical to tokens of different physical types). The Species would correspond to physical types.
The next step in our analogy is to have some Combat Rules. These would correspond to our causal laws. Following Davidson, let’s suppose that all the causal laws are between what physical types the events belong to. That would mean in our game, the Combat Rules are always framed in terms of the Species of the combatants. This makes the game weird. But let’s go along with it. So the idea is that the Combat Rules will say something like: Elves always beat Humans; Humans always beat Orcs; Orcs always beat Elves; and so on.
So now could it be true in this game that a Wizard ever beat a Human in combat? Well, there’s no rule that says what happens when an arbitrary Wizard fights a Human. But the Wizard will belong to Species, and there will be a rule that says what happens when a member of that Species fights a Human. Maybe the Wizard is an Elf, and Elves always beat Humans. So yes, sometimes a Wizard can beat a Human. Other Wizards may be Orcs, and then they wouldn’t beat a Human opponent. This is like the question: can having a headache (mental type of event) ever cause your body to wince, or ingest aspirin, or move from your apartment to the drugstore (various physical effects)? Yes, because some headaches are identical to C-fiber firings (physical type), and there may be Rules (causal laws) that say that events of those physical types will have such-and-such physical effects.
The last element of Davidson’s picture to talk about is why does he think it’s impossible for there to be strict laws connecting mental and physical, that is strict laws of the form:
Every event of mental type M1 causes events of physical/neural type N1.Or laws of the form:
Every event of physical/neural type N2 causes events of mental type M2.Davidson’s thinking here is that there are principles that are partly constitutive of what it is to be a mental state like a belief, desire, and so on. There are also principles that are partly constitutive of what it is to be a physical property like length: for example, length needs to be a transitive relation. That is, if A is longer than B, and B is longer than C, then A has to be longer than C. That’s part of the nature of length, what it is to be a length. (Other physical relations like “is standing directly beside” aren’t transitive.) So the mere fact that there are such constitutitive principles doesn’t yet make mental properties unique.
In the mental case, though, Davidson thinks it’s important that the constitutive principles are holistic. That is, it doesn’t make sense to ascribe someone a belief that there is aspirin in the kitchen if you also ascribe to them a headache, a desire to get rid of the headache, and no intention to go to the kitchen. Unless you also ascribe them a stronger desire to act tough, or you ascribe to them doubt whether aspirin is healthy, or effective at removing headaches, or so on. The basic idea here is that whether it makes sense for a subject to have a belief that there is aspirin in the kitchen depends on what intentions they have, along with what other beliefs, desires, headaches, and other mental states. This is an issue we considered before when discussing behaviorism and functionalism.
Now, none of us is perfectly rational. There are probably some things I believe would be the best thing to do, like go running on Thursday, and don’t have any reason to avoid doing (you go to work early then, so I can’t wake you up), but I don’t have an intention to do. Because I’m somewhat irrational (and in this case, lazy). But Davidson thinks there are limits to how irrational it’s possible to be, or that it makes sense to think someone is. Once there becomes too much of a disconnect between their various beliefs and desires and intentions, it no longer makes clear sense to count those states as beliefs (or at any rate, as the beliefs we thought they were), and desires, and intentions. These constraints about how different mental states have to combine and interact with each other have some “give” or looseness to them, but only some.
This is why Davidson thinks that (p. 122):
[W]e cannot intelligibly attribute any propositional attitude to an agent except within the framework of a viable theory of his beliefs, desires, intentions, and decisions.
There is no assigning beliefs to a person one by one on the basis of his verbal behavior, his choices, or other local signs no matter how plain and evident, for we make sense of particular beliefs only as they cohere with other beliefs, with preferences, with intentions, hopes, fears, expectations, and the rest… [T]he content of a propositional attitude derives from its place in the pattern.
Crediting people with a large degree of consistency cannot be counted mere charity: it is unavoidable if we are to be in a position to accuse them meaningfully or error and some degree of irrationality.
The last sentence is him expressing the idea that if a subject’s states are too incoherent and irrational, it no longer makes sense to count them as beliefs, desires, and so on, with the hypothesized contents, in the first place. He says a bit later:
To the extent that we fail to discover a coherent and plausible pattern in the attitudes and actions of others we simply forego the chance of treating them as persons [that is, creatures with beliefs, desires, and intentions].
Now what does this have to do with whether there can be laws connecting mental types and physical types? Davidson thinks if there could be such laws — and we knew what they were (that’s important) — then we could study how the world is physically arranged and then use the law to judge that the subject must have this mental state, say a belief that there’s aspirin in the kitchen, after all. Without needing to decide or consider what other mental states the subject has.
Here is Davidson on p. 123:
It is a feature of physical reality that physical change can be explained by laws that connect it with other changes and conditions physically described. It is a feature of the mental that the attribution of mental phenomena must be responsible to the background of reasons, beliefs, and intentions of the individual. There cannot be tight connections between the realms if each is to retain allegiance to its proper source of evidence… [W]hen we use the concepts of belief, desire and the rest, we must stand prepared, as the evidence accumulates, to adjust our theory in the light of considerations of overall cogency: the constitutive ideal of rationality partly controls each phase in the evolution of what must be an evolving theory.
And here is Kim’s summary of Davidson’s argument (as expressed there and elsewhere in the paper):
A crucial premise of Davidson’s argument is the thesis that the ascription of intentional states, like beliefs and desires, is regulated by certain principles of rationality that ensure that the total set of such states attributed to a person will be as rational and coherent as possible…
But it is clear that the physical domain is subject to no such requirement; as Davidson says, the principle of rationality and coherence finds “no echo” in physical theory. Suppose now that we have laws connecting beliefs with brain states; in particular, suppose we have laws that specify a neural substrate for each of our beliefs — a series of laws of the form “N occurs to a person at t if and only if B occurs to that person at t,” where N is a neural state and B is a belief. If such laws were available, we could attribute beliefs to a subject, one by one, independently of the constraints of the rationality principle. For in order to determine whether she has a certain belief B, all we would need to do is ascertain whether B’s neural substrate N is present in her; there would be no need to check whether this belief makes sense in the context of her other beliefs or even what other beliefs she has. In short, we could read her mind by reading her brain. The upshot is that the practice of belief attribution would no longer be regulated by the rationality principle… On Davidson’s view, as we saw, the rationality principle is constitutive of mentality, and beliefs that have escaped its jurisdiction can no longer be considered beliefs. (pp. 204-206)