To develop these last thoughts in a more exact way, it will be helpful to borrow the machinery of Ramsification that functionalists have been using ever since David Lewis.49 While Lewis’s method of Ramsifying theories in order to derive functional definitions will be familiar to philosophers at this point, I want to briefly review it here because I will be tweaking Lewis’s original idea just a bit in order to suit my purposes.
Lewis’s original proposal can be illustrated using a toy model. Let T be a theory consisting entirely of the following three clauses.
(i): Tissue damage causes pain.
(ii): Pain causes anxiety.
(iii): Anxiety causes heart rate acceleration.
T, then, is to be understood as the conjunction, (i) & (ii) & (iii). In our model, T’s mental vocabulary consists entirely of two names for mental states, ‘pain’ and ‘anxiety.’ The Ramsey Sentence of T is formed by replacing these mental terms with variables and then prefixing the resulting open sentence with existential quantifiers binding those variables. It looks like this:
The Ramsey Sentence of T: xy(tissue damage causes x & x causes y & y causes heart rate acceleration).
What the Ramsey Sentence of T asserts is that T is “realized,” at least in one sense of this term.50 That is, the Ramsey Sentence of T says that there exist states possessing the various properties and standing in the various relations (both to one another and to other states) that T says pain and anxiety do. On this conception of realization, then, what gets realized in this case is the theory T, while what does the realizing is the n-tuple (or n-tuples) of states satisfying T’s Ramsey Sentence.
The modified Ramsey Sentence of T says that T is not just realized but uniquely realized. For our toy model, it will look like this:
The Modified Ramsey Sentence of T: 1x1y(tissue damage causes x & x causes y & y causes heart rate acceleration).51 With the modified Ramsey Sentence of T in hand, we can now illustrate Lewis’s proposal for deriving functional definitions.
For any possible world w, if the modified Ramsey Sentence of T is true at w then the denotation of the ith mental term occurring in T will be the state which is the ith component of the n-tuple of states uniquely realizing T at w, while if the modified Ramsey Sentence of Tis false at w then the mental terms of T will all be denotationless there. So, suppose that F and G are a pair of states such that, at the world w’, tissue damages causes F, F causes G, and G causes heart rate acceleration. Suppose also that no other pair of states enters into these relations at w’. Then the ordered pair (F, G) uniquely realizes T at w’, and Lewis’s proposal entails that at w’, ‘pain’ (the first mental term occurring in T) denotes F (the first element of the ordered pair uniquely realizing T at w’) and ‘anxiety’ (the second mental term occurring in T) denotes G (the second element of the ordered pair uniquely realizing T at w’). Lewis’s proposal tells us the denotations of the mental terms of T not just at w’ but at all possible worlds, and so if we take meanings to be intensions – construed as functions from worlds to extensions – it provides us with the meanings of those mental terms.
Before we get to my plans for tweaking Lewis’s account, I want to make a quick point about the primitive vocabulary of theories being Ramsified. Given a particular Ramsification of a theory, those theoretical terms that aren’t replaced by variables in the formation of the theory’s Ramsey sentence comprise the primitive vocabulary of the theory, relative to that Ramsification. In our example, T’s primitive vocabulary relative to the way in which we’ve Ramsified it would be ‘causes,’ ‘tissue damage,’ and ‘heart rate acceleration’ (in addition to the logical terms figuring in T). In emphasizing that the primitiveness of a vocabulary is relative to a particular Ramsification, I mean to be covering two separate but related points.
First, the theoretical terms that are primitive relative to a given Ramsification need not be primitive in any absolute sense. Thus, in adopting the Ramsification of T that we have, we are in no way committing ourselves to the view that ‘causes,’ ‘tissue damage,’ and ‘heart rate acceleration’ are themselves completely undefinable.
Second, and more interestingly for my purposes, there will always be more than one way to Ramsify a theory, and the vocabulary that is primitive relative to one Ramsification need not be primitive relative to another. So, for instance, an alternative Ramsification of T would have us leave the mental terms ‘pain’ and ‘anxiety’ untouched while replacing the term ‘causes’ with a bound variable.52 This would be the way to proceed if what we wanted to do was define causation as the relation that obtains between tissue damage and pain, between pain and anxiety, and between anxiety and heart rate acceleration. Of course we wouldn’t really want to do this, but set that aside.
The point I want to note here is that there’s nothing in principle to prevent us from adopting one Ramsification of a theory in order to use a first subset of the terms of that theory (the primitive vocabulary relative to that Ramsification) to define a second subset of terms, and then turning around and adopting a second Ramsification of the same theory in order to use that second subset of terms (the primitive vocabulary relative to the second Ramsification) to define the first subset of terms. If we were to make both of these moves, we would be embracing a kind of circularity in the functional definitions obtained, but perhaps such circularity needn’t be objectionable. If we thought that the two subsets of theoretical terms were interdefinable and equally basic, going in for the two rounds of Ramsification would be a way of capturing this.
Now, this opportunity to Ramsify twice over will be declined by standard functionalists, who take one of the chief appeals of functionalism to be its promise of defining mental terms in completely non-mental terms (i.e., terms that are neither mental themselves nor defined in mental terms). For reasons we’ll see at the end of this chapter though, it’s at least not obvious that the view I’ll be defending should follow standard functionalists on this point. It may be that the most plausible way to develop my position involves embracing something like the circularity in question. We’ll discuss these issues more below. Here, I just want to flag the point to set up that later discussion.
Now let’s turn to the ways in which I’ll be adjusting Lewis’s original proposal. The reason adjustment is required is because Lewis, as a nominal essence functionalist, is offering a recipe for functionally defining mental terms, while I, as a real essence functionalist, am not directly interested in definitions. I need to find a way to convert Lewis’s original semantic proposal into a kind of metaphysical proposal, then. In carrying this conversion out, the idea I want to guide us is that folk psychology purports to provide a complete list of the essential features of mental states, and thus to specify the real essences of those states. So, for instance, imagine that folk psychology just were the theory T we’ve been considering. Then according to my guiding idea, part of what folk psychology says, in effect, is that the essence of pain is to be the state caused by tissue damage and causing anxiety. If we could then find some state having this essence – which requires, at a minimum, that the state in question possess these features in all possible worlds – folk psychology would license us to identify pain with that state.
Perhaps the most straightforward way we could try to convert Lewis’s original semantic proposal into a metaphysical one successfully capturing these thoughts would be to construe properties themselves as functions from worlds to extensions and then identify those functions obtained using Lewis’s original method with the appropriate mental properties. So, for instance, we would take the function from worlds to extensions that Lewis identifies with the meaning of ‘pain’ and we would instead identify it with the property of pain itself. This, in effect, is what role-state functionalists do.53 To a first approximation, it’s what I want to do as well.
There are several potential objections to the sorts of mental property identifications we are presently contemplating, but for the time being I want to focus exclusively on the one I accept.54 I accept a fine-grained conception of properties according to which necessarily coinstantiated properties can be distinct. What’s more, I regard this conception of properties as a nonnegotiable element of nonreductive physicalism – not just the version I will be defending, but standard alternative versions as well. Without arguing for this conception of properties just yet, let me note that if I’m right and properties slice things more finely than necessary coextensionality does, then we won’t generally be able to identify properties with functions from worlds to extensions – they’re too coarse-grained.55 This point now having been noted, in this work we’ll often be able to make simplifying assumptions which allow us to ignore it. When those assumptions are in place, my view in effect is, again, that mental properties are identical to the functions from worlds to extensions obtained using Lewis’s method.