To: Joe H.
From: Geoffrey Klempner
Subject: Mind-body problem and the definition of identity
Date: 25th November 2009 12:54

Dear Joe,

Thank you for your email of 18 November, with your second essay for Pathways Philosophy of Mind, in response to the question, 'What is Identity? What is the relevance of a definition of 'identity' to the problem of the relation between mind and body?'

I understand your frustration with the 800 word limit. This was actually created as a liberating device, to enable students who would otherwise have difficulty 'composing an essay' to set themselves an achievable target. However, I also happen to believe that 800 words is -- or can be, when effectively deployed -- a beautiful format. It is no accident that the target length for my replies is the same 800 words.

You have tried to pack in as much as possible, but you could have helped yourself by focusing more closely on the question itself. We are not concerned with evaluating particular mind-body theories but rather with laying out the ground rules for the debate over the question of identity.

What is identity? I know that Leibniz Law is often trotted out as 'the' definition of identity, but it has an inherent problem. The biconditional x=y <-> (F)(Fx <-> Fy) splits into two principles, the Identity of Indiscernibles (reading right to left) and the weaker reading of Leibniz Law (reading left to right). On the weaker reading, if x=y then all and only properties of x are properties of y. Whereas the Identity of Indiscernibles is only remotely plausible if we include spatial location as a 'property', which effectively begs the question.

What does this mean for mind-body identity theories? We can only use the weaker version of Leibniz Law, which merely gives the consequences of an identity statement. However, consider Kolakowski's statement about my ear and the moon (you can find the quote at Follydiddledah http://www.follydiddledah.com/image_and_quote_4.html together with a nice illustration).

I claim that my ear IS identical with the moon. 'How come,' you say. 'What I mean is that in 1969, Neil Armstrong walked on my-ear-and-the-moon, the annoying hairs which grow on my-ear-and-the-moon need trimming regularly, and so on.'

This is really no different from what Armstrong and Smart are doing, metaphysically speaking. Two things are always two things, however hard one tries to push them together. Using the magic word 'identity' gets you nowhere.

So the next question is, What more is needed to explain identity, if Leibniz Law (on the weaker reading) won't suffice? This is where one gets to talk about the nature of particulars, the role of identity over time, and the difference between existing particulars and events.

We also get to look at so-called 'property identity': are we still talking about identity here? Properties can be co-extensional, determining the same set, or (in some sense) necessarily co-extensional. For Armstrong and Smart, the attraction of type identity (property identity) is that it entails token identity. If earache IS 'stimulation of c-fibres' then THIS earache is an actual, physical process going in in my brain, nothing more.

I've heard it said that you can have a kind of property identity, in a weaker sense which does not imply token identity of either particulars or events. So if you are keen on preserving intuitions about qualia, you can keep these and also sound respectably 'materialist' in your talk of mind. This looks like a cop-out to me.

So we are back to the question, what IS identity? If Leibniz Law only gives the consequences of identity then we need to focus on how particulars are picked out and identified, at a time or over time. And this is where the whole issue of 'qualia' or 'private objects' arises because if you have gone so far to 'pick out' a quale or a private object then (as I would argue) it is too late to make claims about identity.

Some would object to this as inserting an unacceptable epistemological bias into logic. But logic has to be applied to the world otherwise it is toothless. (For more on this topic see David Wiggins 'Sameness and Substance' Blackwell.)

Kripke is central because he identifies the key aspect of the notion of qualia which is relevant to the mind-body question: the idea that my knowledge of my quale is 'de re' rather than 'de dicto'. It is direct, unmediated by a description; in any possible world it could not be anything but what it is.

On the general topic of types and tokens in relation to the mind-body problem, I would advocate abandoning the confusing terminology of 'types' and 'tokens' and concentrate on the question of identity.

Consider the world of abstract objects. Is the five, as Frege believed, an entity? Does 5 exist as an abstract object? That's a meaningful question. It is clear what the difference is between regarding 5 as a second-order property defined in predicate calculus, and regarding 5 as existing in its own right as an entity with an identity. Talk of 'tokens' and 'types' has a role only in relation to mathematical symbolism -- names for numbers -- not for numbers in themselves.

All the best,

Geoffrey