Now that we’ve gone over several important points of divergence, I want to shift the discussion to the primary point of convergence between Davidson’s position and the one I’ll be defending in this work, the idea that the mental realm is governed by constitutive principles of rationality. Call this the constitutive rationality thesis (CRT). In the present chapter I’ll be explaining in as precise terms as possible what I understand the (CRT) to mean. Once we’re clear on what it means I’ll use Chapter 3 to argue for the (CRT)’s truth and Chapter 4 to argue that its truth (together with other defensible premises) entails the mental’s irreducibility to the physical.
In order to explicate the (CRT) I find it useful to rely on the idea one finds in functionalist works, that there is a certain psychological theory that specifies the essences, in some sense, of mental states. Later on I’ll be taking pains to distinguish my view from standard versions of functionalism. At least as a first approximation, however, the view I’m defending can be usefully thought of as a special kind of functionalism. Casting myself as a functionalist, then, I want to use the present section to say a few things about the kind of functionalist I am.
While all functionalists can be construed as holding that there is a certain psychological theory that specifies the essences, in some sense, of mental states, they disagree among one another as to what the source of that theory is. According to commonsense functionalists, the specifying theory is a priori and is somehow grasped by all ordinary people.43 Perhaps this folk psychological theory is derivable from platitudes about mental states that everyone recognizes as true. Perhaps instead it is as internally represented theory, not unlike an internally represented grammar, in which case the clauses of the folk theory needn’t be any more platitudinous than are the grammatical rules we readily employ when communicating but have trouble explicitly articulating.44 Either way, the idea here – that the folk know the specifying theory (at least tacitly) – is notably opposed by psychofunctionalists, who claim instead that the specifying theory is a posteriori and comes from (a perhaps completed version of) empirical psychology.
There are, I believe, compelling (and widely known) reasons to be a commonsense functionalist as opposed to a psychofunctionalist.45In this work, I’ll be taking a commonsense functionalistic framework for granted. This means that in settling questions about the essences of mental states, I will be assuming without serious argument that the proper methodology to use is to appeal to shared modal intuitions about those states. That is, as opposed to appealing to the sorts of empirical results produced by, say, cognitive psychology. This being said, I won’t be completely ignoring empirical findings in this work. In particular, in Chapter 3 I will address how the (CRT) is to be reconciled with the massive psychological literature detailing human beings’ systematic irrationality.
Again, all functionalists agree that there is a psychological theory specifying the essences, in some sense, of mental states. But in what sense, exactly? On this there is disagreement. According to what I will be calling nominal essence functionalists, what the specifying theory does is fix the meanings of mental terms. Mental terms have functional definitions, on this view. According to what I will be calling real essence functionalists, on the other hand, what the specifying theory does is fix the underlying metaphysical natures of mental states. Mental states have functional (real) essences, on this view.46
To the extent that my view is properly categorized as a kind of functionalism, it is a version of real essence functionalism. I will be arguing that mental states have functional essences of a sort, and that this essence precludes their being reducible to physical states. In this work, I won’t directly be addressing the nature of the meanings of our mental terms. Perhaps ‘belief’ is a disguised rigid description which means, roughly, the mental state having the real essence that the specifying psychological theory says belief has. Or maybe ‘belief’ just means belief – that is, the state having the real essence that the specifying psychological theory says belief has.47 Each of these views (among others) is compatible with the view I’ll be defending here.
Putting together the two positions I have staked out in this section: I am a commonsense, real essence functionalist. I take there to be a folk psychological theory that posits the existence of various mental states having certain specified real essences. If the world turns out not to contain states possessing those essences, then it follows that folk psychology is in error and the mental states it posits don’t actually exist. If, on the other hand, the world turns out to contain states possessing the essences in question, then it follows that those states just are (that is, are identical to) the mental states folk psychology posits.48