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Friday, February 25, 2005

Strong Composition as Identity as an Answer to the General Composition Question

Some philosophers have put forward a thesis that has been called "Composition as Identity". Among those who have supported this thesis are Donald Baxter, David Lewis, and D.M. Armstrong. According to this thesis, composition is (in some way) importantly like identity. There are many characteristic ways to try to get across the underlying idea of Composition as Identity. For instance:
A fusion just is its parts; the parts just are their fusion.
A fusion is nothing over and above its parts.
Once one has accepted the existence of the parts, one incurs no further commitment by accepting the existence of their fusion.

In this entry, I will characterize a particular version of Composition as Identity, which shall be referred to as "Strong Composition as Identity", and I will offer a framework for understanding this thesis in terms of the General Composition Question.

Prior to stating Strong Composition as Identity (SCAI), it will be helpful to have certain assumptions of the view on the table. The first of these is that identity is a two-place relation that is reflexive, symmetric, and transitive. Like other relations, though, identity does not obtain merely between individuals, but may also obtain between some things; that is, some things may be identical to some other things. So, for instance, Mark Twain, Mary Ann Evans, and Hesperus are identical to Samuel Clemens, George Eliot, and Phosphorus. And Greg and Mary are identical identical to Greg and Mary.

Thus far this should all be relatively uncontroversial. Although some may be uncomfortable with plural properties (and even plural predicates), it does seem right to say that, for any things, those things are identical to themselves. However, proponents of SCAI go further. Not only can individuals be identical to individuals and some individuals to some individuals, they say, but individuals may be identical to some individuals and some individuals may be identical to an individual.

Admittedly, this is an odd view and (I think) is almost certainly internally inconsistent. However, putting that aside, let us now state SCAI:
(SCAI) Necessarily, for any xxs and for all y, the xxs compose y iff the xxs are identical to y.
In other words, the parts of a thing, taken jointly, are identical to that thing. So, for instance, on this view, my head, my arms, my legs, and my torso (taken jointly) are identical to me.

Having said this, we may ask certain questions concerning SCAI. For instance, how does SCAI fit into a general theory of the part-whole relation? As follows, I think:

Philosophers who are concerned with these things tend to distinguish between the Special Composition Question and the General Composition Question. The Special Composition Question asks, basically, under what circumstances composition occurs. More precisely, it asks what correct and informative conditions can be given to fill in the blank in the following schema:
Necessarily, for any xxs, there is a y such that the xxs compose y iff ________.

On the other hand, the General Composition Question is not concerned with the circumstances under which composition occurs, but rather with what composition is. That is, it is concerned with the correct analysis of composition. More precisely, it asks what correct and informative conditions can be given to fill in the blank in the following schema:
Necessarily, for any xxs and for all y, the xxs compose y iff ________.

My suggestion for understanding SCAI, then, ought to be pretty obvious: it is an attempt at an answer to the General Composition Question. In addition, I think, it is an answer to the General Composition Question that is consistent with just about any answer to the Special Composition Question (except an answer that entails that necessarily, for any xxs, there is a y such that the xxs compose y iff it is not the case that there is a z such that the xxs are identical to z).