Our present topic, one that is central to metaphysics in the view of many metaphysicians, is continuants: objects that persist through time. The chief puzzle that continuants give rise to is that, while they are self-identical over time, their properties change over time. I am same person I was 50 years ago, but I'm not the same height.

One kind of solution to the problem faces up to it, and thinks of properties as occurring at times while the object persists because it retains something essential.

Quine's solution falls into a different family of solutions known collectively as four-dimensionalism. It is pretty easy to give a coherent four-dimensionalist account of objects without falling into traps about, for example, change, since, on four-dimensionalist accounts, there is no change. "Change" is explained away as merely different properties at different times. The main objection to four-dimensionalist accounts is exactly that: they don't account for persistence, change, the flow of time, the present moment, and the like.

The other problem with four-dimensionalist accounts is that we just don't ordinarily think of objects that way. The view is revisionist. It is therefore saddled with giving an account of how we ordinarily do think, what the status of that ordinary conception is, and so forth.

How do we learn to identify a persistent, extended object? Well, once we have learned enough of a theory, we can do it via descriptions, causal dubbing, and probably other means, but initially, it seems obvious, we must learn how to do it by being presented with lots of examples and being corrected: we get a large set of examples at different places and times that all count as being examples of the same object.

So far, Quine hasn't said much new. He observes:

• The same experience can count as different objects. (Same river; same water.)
• Simple predicates can be learned in exactly the same way. (Red.)

The first of these points is much simpler to make sense of four dimensionally: it is familiar fact that objects can overlap or include one another in space; the point is just the same in time.

There are familiar disconnected objects, like suits, pairs of shoes, the territory of the United States. Since we accept those, we could perfectly well, Quine points out, accept red as a like kind of object, though, of course, that would be revisionary.

Quine sets the puzzle, why don't we talk about red in that way, and how does the way in which we do talk about red differ?

The main difference, unsurprisingly, given that a river is an object and red is not, concerns identity: When we learn to distinguish examples of the Mississippi River from other things, we take them all to be examples of the same object—the river. When we, similarly, learn to distinguish examples of red things, we do not learn to take them as parts of the same object.

Why do we have these two different practices? That is a historical, psychological, and linguistic question that we have no idea how to go about answering, but Quine suggests a basic difference between the two kinds of practices that can motivate both, and conjectures that that plays a role in the real story.

• When we have no need to distinguish things, it is simpler to identify them, take them to be one. (That motivates the thing practice.) Note that the motivation is, at base, pragmatic and relative to interests.
• The red "trick" doesn't work for shapes. Hence we need the property practice.

Quine's idea yields many important results:

• Properties are not objects.
• We can use objects instead of some simple properties, which suggests a Just So story about why many languages treat properties like objects in various grammatical respects. (Example: Hesperus is Phosphorus. Hesperus is small and glowing. "The 'is' of identity, and the 'is' of predication.)
• Our ability to learn about objects and properties relies on our have similar faculties of discrimination to those we are learning from. (Otherwise, too many examples would be needed.)
• The difference between objects and properties, on the other hand, is something rather linguistic in nature: the notion of identity.
• What we take to be objects is largely pragmatic.

Thus, what there is, in the grand sense of what there is according to our whole conceptual scheme, is not tested by comparing the scheme to an external world. Rather, we live in a world using a scheme and each exerts pressure on the other, which, we hope, wears them into a better fit as experience continues.

-- ShaughanLavine - 07 Oct 2008