Is a Thing Just the Sum of Its Parts
Hughes (Christopher)
Source: Proceedings of the Aristotelian Society, New Series, Vol. 86 (1985 - 1986), pp. 213-233
Paper - Abstract

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Author’s Introduction

  1. In what follows, I shall defend the view that a (composite) physical object is just the mereological sum of its parts. I do not claim that the aggregative conception of physical objects I favor is the sole defensible one, only that it is at least as attractive as its competitors.
  2. My focus will be an argument to the effect that an aggregative conception of physical objects is untenable. That argument goes like this:
      A sortally1 individuated composite thing (say, Lake Cayuga) is a trans-world continuant, which exists at a number of times, and in a number of different possible worlds, and is composed of different parts at different times and in different worlds. An aggregate is a trans-world continuant of another sort, which is composed of exactly the same parts at all of the times, and in all of the worlds in which it exists. Hence a sortally2 individuated composite physical object (like Lake Cayuga) is not the same as the aggregate of its parts.
    Because arguments of this kind are found so often in the literature, I shall call the above argument the standard argument, and its conclusion the standard view (on the relation of sortally3 individuated continuants to aggregates). The standard argument relies on a conception of sortally4 individuated composita as genuine trans-world continuants, and I shall try to show that it is better not to think of sortally5 individuated composita in this way. If we do not, I shall argue, the case against identifying physical objects with the aggregate of their parts looks quite weak.
  3. The standard argument splits up into two arguments against identifying sortally6 individuated composita with aggregates: the argument from existence at different times, and the argument from existence in different worlds. The former exploits the fact that - if we are thinking of aggregates as mereological aggregates of ordinary (micro) continuants - a sortally7 individuated continuant will almost invariably fail to have the same world line as any aggregate. There are various ways of trying to maintain in the face of this argument that sortally8 individuated continuants are aggregates of ordinary (micro) continuants. I don't think any are promising; but considerations of space prevent me from considering their merits here. The best response to the argument from existence at different times is to concede it a limited victory: it shows that sortally9 individuated continuants are not aggregates whose parts are ordinary continuants. To say this, however, is not to accept the standard view. For it might be that physical objects are mereological aggregates, but not aggregates of continuants. Or it might be that composite physical objects are aggregates of continuants, and that lakes, statues10, and the like aren't identical to any physical object. I shall have something to say about each of these options later; but first I shall consider an argument purporting to show that a sortally11 individuated continuant can be distinct from an aggregate, even if the continuant and the aggregate share a world line.


From "Noonan (Harold), Ed. - Identity".

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