Composition as Identity

Unrestricted Mereologists claim that whenever we have two things, x and y, there is a further thing, z, which is their mereological fusion. One complaint against unrestricted mereology is that its ontological costs are too high: for any two (non-overlapping) things in our universe, the mereologist will claim that there is a third (its fusion). And once we add fusions, we can also add fusions of fusions, and so on. To escape the charge of ontological extravagance, many mereologists have insisted that their view is ontologically friendly. One way to do this is to advance Composition as Identity (CI), which claims that the fusion of x and y is not a third thing, distinct from x and y, but is identical to x and y. But, we might wonder, how could the fusion of x and y fail to be a third thing, distinct from x and y? Much of the current philosophical literature on mereology and composition is dedicate to criticisms of CI. In my dissertation, I proceed systematically, taking on the objections to CI one by one, showing how this view can be defended and plausibly developed. Common to most of these objections, I argue, is that they all fail to take into account two important resources available to the proponent of CI. First, many ignore the availability of a plural logic and language, complete with plural quantifiers, plural predicates, and (perhaps most importantly) a plural/singular hybrid identity predicate. Second, none of them considers what I call plural counting, whereby our counts of objects are not constrained by singular quantification and singular identity statements. I show how these two resources can bolster a strong defense of CI, securing that mereology is, after all, ontologically innocent. In addition, I show how CI has the advantage of providing elegant solutions to an array of problems in philosophy: perception puzzles, problems of prevention and causation, shadow puzzles, and Frankfurt puzzles about moral responsibility. I also introduce a metaphysics of objects that, together with CI, addresses modal worries, including issues concerning CI and merelogical essentialism