Thursday, 23 June 2011

Sketch of a Way of Thinking about Modality - Part 1

[UPDATE: This sketch, except for parts of part 2, will soon be made mostly redundant by a paper I am working on. I expect to make a draft of this paper available in early November. A link will appear here. - TH 13/10/2011]

[UPDATE 2: The paper mentioned above is here.]

[UPDATE 3, March 2013: What appears below has been left so far behind that I'm almost embarrassed about it. For my latest on these topics, see An Account of Subjunctive Necessity.]

This is the first installment of a two-part series of posts where I aim to sketch some ideas about modality which will feature in a book I am working on, Necessity and Conceptual Systems. The material is still very much under development, and I apologize for the obscurities which the reader will inevitably find in it. Comments and criticisms are very welcome.

In this first part, I will introduce the approach, and indicate how it handles the necessary a posteriori, using 'Hesperus is Phosphorus' as a case-study. In part 2 I will discuss the notion of de re modality, of essence, and natural-kind examples such as 'Water is H20', as well as some more general issues which arise on my approach (especially to do with epistemic modality and ascriptions of intentional content).

In the Golden Age of analytic philosophy, necessarily true propositions were widely taken to be those which are satisfied by (or 'come out true' on) all configurations of some conceptual or linguistic system. Possibility was understood in terms of satisfaction by at least one configuration. Our conceptual system, our means of understanding the world, is here thought of as something like a model, or a machine, which has moving parts, and which can be put into various positions or configurations. Each configuration can be thought of as corresponding to, or satisfying, or even being, a set of propositions. (I have taken many liberties in the formulation of this description.)

Conceptual or linguistic systems of the kind in question were thought to be describable with "semantical rules" for a language, and necessary propositions were thus commonly taken to be a priori and true "in virtue of the meaning" of the terms involved (cf. Carnap's Meaning and Necessity, Ayer's Language, Truth and Logic). This yields a notion of necessity reminiscent of the notion of truth-functional tautologousness. (Earlier, in the Tractatus - which was a major inspiration to both Ayer and Carnap - this relationship is much closer than mere reminiscence.)

This sort of view was attacked by Quine in at least two ways (cf. his 'Truth by Convention', 'Two Dogmas of Empiricism'). Quine's undifferentiated picture of language had a sobering or worrying effect, but it did not stop people carrying on with some version of the view in question. This is connected with the fact that it amounted to a kind of quietism or abstinence with respect to the relevant sorts of notions (semantic, modal), rather than a sustained attempt to attain positive insight about them.

The really decisive blow to the Golden Age view of modality came from Kripke. His fundamental contribution was to persuasively argue that the a priori does not coincide with the (metaphysically) necessary, and relatedly, that epistemic modality ("what could be the case") is to be distinguished from metaphysical modality ("what could have been the case" in a certain unrestricted sense). This contribution was closely bound up with Kripke's ideas concerning naming and reference, more on which in a moment. The recognition of the necessary a posteriori in particular, and the associated idea that conceivability doesn't entail possibility, has led to a reaction against views of modality of the Golden Age sort.

(About 'metaphysical modality': one sometimes hears it said of a philosopher that they countenance metaphysical modality, as though this indicates that the person holds some sort of doctrine, which may be quite esoteric. But 'metaphysical modality' is just a label for me - synonymous with 'subjunctive modality' - for a notion "detected" in the logic of language. That said, someone who felt this notion was, e.g., a trivial artifact of the way we happen to talk, rather than a deep artifact of the way we think, would probably not want to use this label.)

My approach to modality retains the view that necessity - metaphysical necessity - can be fruitfully understood in terms of invariance through all configurations of a conceptual system. But it also takes Kripke's separation of the a priori and the metaphysically necessary fully to heart. This latter point is one respect in which my approach differs from that of the two-dimensional semanticists. Another key contrast is that the possible worlds framework is not fundamental to my view.

Broadly speaking, I handle the necessary a posteriori by doing two things. Firstly, I work with a much more fine-grained notion of 'conceptual system' than did the logical empiricists. (The sense of 'fine-grained' here should become clearer in a moment.) Secondly, I embrace a certain kind of semantic externalism - roughly, the view that sense doesn't determine reference (other ways to put this which for me are roughly equivalent: intension doesn't determine extension, concept doesn't determine object).

I will illustrate how this works with respect to a classic example of the necessary a posteriori: 'Hesperus is Phosphorus'.1

I follow Kripke in holding that proper names do not have reference-determining senses (which hangs together with semantic externalism via Putnam's idea of Twin Earth), and also that proper names do not have a semantics which can be given in the form of general conceptual content such as definite descriptions, or clusters thereof (irrespective of whether this content can be said to determine reference).

I do not, however, accept the (to my mind very strange and confused) idea that proper names are 'mere tags' (Ruth Barcan Marcus's phrase), that all there is to the meaning of a name is its referent, etc. This idea is sometimes associated with Mill's claim that names have no 'connotation', only 'denotation', and also with the phrase 'direct reference'.2

We have individual concepts - concepts of individuals, of particular objects - and we often associate these with proper names. This sheds light on Kripke's rigid designation thesis (the thesis that a referring proper name designates the same object in all possible worlds at which that object exists). If names are associated with individual concepts - concepts of particular objects - then it is immediate that they will designate the same object in all possible worlds where that object exists; designating another object is out of the question, since we are holding fixed the associated individual concept. We may thus distinguish rigid designators such as ordinary proper names, which designate rigidly because they are directly associated with individual concepts, from other rigid designators such as definite descriptions in mathematics.

Once we recognize individual concepts in this way, we can say that when someone accepts that Hesperus is Phosphorus (having previously taken them to be distinct), there is a change in their conceptual system - in the relevant fine-grained sense. Of course, in a more coarse-grained (and more ordinary) sense, we can say that they have before and after the same conceptual system. The fine-grained change consists in the unification of two individual concepts. The original concepts, we might say, are not blended irrevocably but remain as aspect-concepts united under a common master. From now on, it should be kept in mind that conceptual systems will usually be individuated here in this fine-grained sense.

In the former conceptual system (call this 'the Babylonian system'), where the Hesperus-concept is separated from the Phosphorus-concept, the distinctness of Hesperus and Phosphorus is invariant through all configurations of the system; if one positively believes that Hesperus and Phosphorus are distinct, one will say that, although it might conceivably turn out that Hesperus is Phosphorus after all, given that it isn't, Hesperus could not have been Phosphorus. (And one will of course be wrong.) In the latter conceptual system (call this 'our system'), where the Hesperus- and Phosphorus-concepts are unified, the identity of Hesperus and Phosphorus is invariant through all configurations of the system; when one knows that Hesperus is Phosphorus, one will say that, although it might conceivably turn out that Hesperus is distinct from Phosphorus after all, given that it isn't, Hesperus could not have been other than Phosphorus.

Now, with our fine-grained understanding of conceptual systems in place, I maintain that we can still say that all (metaphysically) necessarily true propositions are satisfied by all configurations of their host conceptual systems. We can even say that a truth is metaphysically necessary iff it is satisfied by all configurations of its host system. We just can't say that all propositions which are satisfied by all configuration of their host systems are necessary truths. So far, then, we can say what distinguishes necessary from contingent truths, but we can't say what distinguishes necessary truths from other proposition which are satisfied by all configurations of their host systems - we might call these 'false propositions of necessary character'. What can we say that will do this?

I think we can say something like: a proposition P is necessarily true iff it is satisfied by all configurations of its host system and the concepts involved in P are jointly adequate to their objects with respect to P.

First I want to say that I am not concerned to provide a reductive analysis of modal concepts. Relatedly, I am happy for the relevant modal notions and my ternary relation of 'adequacy' to be explanatory of each other; I do not suppose it is a one-way street, where my notion does all the explaining, nor do I take my notion to be more "fundamental" in any metaphysical sense. I am interested in showing (and making) connections.

I will make a start at explicating the above proposal by indicating how it applies to the 'Hesperus is Phosphorus' case. In the Babylonian system, the Hesperus-concept and the Phosphorus-concept are not unified (are taken to represent distinct objects), but they both have the same object, the same extension, and so together (jointly) they are inadequate to their objects with respect to 'Hesperus is not Phosphorus'. So their proposition 'Hesperus is not Phosphorus' fulfills the first condition given above, before the 'and' - it is satisfied by all configurations of their system - but it does not fulfill the second. Our Hesperus- and Phosphorus-concepts, which also have the same extension, are in contrast united, as aspect-concepts, under a common master concept (the concept of Venus). Hence they are adequate to their objects - or object - with respect to our proposition 'Hesperus is Phosphorus'.

Why do I not simply say that a proposition is necessarily true iff it is satisfied by all configurations of its host system and its concepts are jointly adequate to their objects? Why do I add 'with respect to that proposition'? I will explain this with an example. Assume for the sake of argument that Hesperus (Venus) is necessarily not intelligent - i.e. that Hesperus could not have been intelligent. Now, suppose someone believes that Hesperus is intelligent, and necessarily so - loosely speaking, that it is part of their concept of Hesperus that it is intelligent. In that case, their concept of Hesperus would not be adequate to its object with respect to 'Hesperus is intelligent'. But they may know, for all that, that Hesperus is Phosphorus, and so their concepts of Hesperus and Phosphorus might be jointly adequate to their object with respect to 'Hesperus is Phosphorus'.

Conversely, someone may know that Hesperus is necessarily not intelligent, while mistakenly believing that Hesperus is not Phosphorus, thus having an adequate conceptual situation with respect to propositions about the intelligence of Hesperus, but not with respect to propositions about the identity of Hesperus and Phosphorus.

Speaking broadly, necessity is, on this understanding, not simply a matter of a proposition having a certain status in a conceptual system. It is, as well as that, a matter of the system being adequate to its objects with respect to that proposition. The adequacy of some set of concepts to their objects obviously depends on the identity (and nature) of those objects - and this is not in general determined by the system. (This is how semantic externalism fits in.) Hence you cannot, in general, tell simply by looking at a proposition in a system whether or not it is necessarily true - there are a posteriori necessities.


The compatibility of externalism with rigid designation
(Postscript added 14 August, 2011.)

It may look as though there is a tension between my externalist claim that the extension of an individual concept is not in general determined by the concept itself, and the claim that names rigidly designate: if names are tied to individual concepts, and individual concepts do not in general determine their extension, it looks like a given individual concept can have different extensions in different environments. This is so (at least, when we individuate concepts internally) but there is no real tension here: the rigidity applies to names in use - names tied to token individual concepts embedded in an environment. Individual concepts are not like general concepts: the whole point of them is to apply to one particular object. And so the contrast between names and definite descriptions remains: when we consider counterfactual scenarios and hold the meaning of our terms fixed, our names which are tied to individual concepts always refer to 'the same object'.

This is all perfectly compatible with the fact that the same concept, in a different environment, might be connected up to a different object. The extension of our individual concepts may in some cases even change over time: if an object we know is replaced with a substitute, and we don't notice, after a while it will become true to say that our individual concept has changed its extension. But we don't let the extension change "across possible worlds" when representing counterfactual scenarios using a particular individual concept in a particular environment.

Part 2.

Individual concepts are under-discussed in contemporary philosophy. For further online reading on what they can do, see:

- My post at Philosophy, et cetera, 'An advertisement for individual concepts'

- A recent article by linguist Barbara Abbott, 'Support for Individual Concepts'.

- John McCarthy's article, 'First Order Theories of Individual Concepts and Propositions'. (Warning: arguably contains some use-mention confusion.)

Interestingly, neither of these authors are (primarily) philosophers.

1 I pass over one well-known issue here, to do with the fact that Hesperus/Phosphorus might not have existed. There is a discussion of this on Greg Frost-Arnold's blog. If one is really worried about this, consider instead the example 'If Hesperus exists, then Hesperus is Phosphorus'.
2 It should be noted, however, that Mill's claim is appropriate if 'connotation' is interpreted to mean 'reference-determining sense' or 'general conceptual content', and likewise that the phrase 'direct reference' is appropriate if 'direct' is interpreted to mean 'not via general conceptual content' or 'not via reference-determining sense'.