Lynch's Role-Functionalism About Truth

Michael Lynch visited Arche recently and gave two great seminars on alethic pluralism, defending the view that truth is "both many and one" in the sense that truth is a multiply realizable functional property. This post is an attempt to record some of the thoughts I had in the discussion period about one of the arguments we looked at (which can also be found on p.15 of this online manuscript).

Michael proposes that '[i]n general, a real distinction between a property and a concept is merited whenever there are features relevant to something's being F which go beyond what can be known just by reflecting on our concept of Fs.' He also notes that '... according to alethic functionalism, a proposition is a member of the truth kind in virtue of its having the supervenient role property of truth.' But the nature of the realizing property, and whether a proposition has it, 'go beyond' the concept of truth, in that 'mere reflection on the concept of truth does not reveal them'. Therefore, Michael concludes, the property of truth is not a 'mere construction out of the concept'.

In our seminar I raised the concern that two readings of the intial claim are available, only one of which is plausible, although the other seems to be relied upon during the course of the argument. The two readings are:
1. Property and concept are distinct if there are features relevant to something's being F such that whether they are relevant to something's being F is not knowable just through reflection on the concept of truth.
2. Property and concept are distinct if there are features relevant to something's being F such that whether something has those features or not is not knowable just through reflection on the concept of truth.

One thing to note about whatever reading we settle on (this point was made by Crispin Wright during the seminar) is that we must be careful with the notion of 'relevance' here. We don't mean causal or explanatory relevance, for instance. (Any property F, even one which is just a reflection of our concept, could be such that part of the explanation of why a particular thing is F appeals to features of that thing which 'go beyond' - in either sense - reflection on the concept of F.) Something more like constitutive relevance seems to be needed. ('Constitutive' relevance needn't entail any kind of knowability through conceptual reflection - compare e.g. the kind of relevance that the feature of being H2O has to the property of being water.)

Suppose we can settle on an appropriate notion of relevance. Still, even if 1 is plausible, 2 surely isn't. 2, however, seems to be what's at work when it's claimed that it is significant that whether a proposition has some realizer property is not knowable just by reflection on the concept of truth.

Nonetheless, might it be significant that the nature of the realizing properties is not knowable through reflection on the concept of truth? I'm not sure. To convince me that it is, Michael needs to argue that the 'relevance' of the realizer properties to the property of truth is not comparable to causal or explanatory relevance, but is such as to make the realizer properties constitutively relevant to the role property.

But I think there may be a dilemma lurking here. If something about the realizer properties were constitutively relevant to the role property, such that this relevance wasn't knowable just through reflection on the role property, wouldn't that mean the role property was no longer purely functional in nature?

Compare: the Twin Earth thought experiment convinces us that being H2O is (although this fact is not knowable by conceptual reflection) constitutively relevant to being water. But at the same time it convinces us that being water isn't just a matter of being the colourless liquid that flows in our rivers etc.. Similarly, if something convinces us that (say) some fact about the nature of correspondance or coherence is a posteriori constitutively relevant to the property of truth, won't that simultaneously convince us that being true is not just a matter of having a property which fulfils the truth-platitudes that Michael wants to use to characterize truth's functional role?