But What Kind of Thing is a 'Fusion'?: Circular Reasoning in Sider’s Argument from Vagueness
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Ordinarily, we suppose that material objects sometimes do, and sometimes do not, form a further object. In his book Four-Dimensionalism, Theodore Sider develops an argument that attempts to show this assumption is mistaken. Sider’s argument from vagueness is one of the most influential arguments in support of universalism, the thesis that composition is unrestricted: whenever some concrete entities exists, so does their mereological fusion. The argument from vagueness is defective – I submit – because it begs the question. Sider distorts the notion of a ‘concrete object’ so that it does not coordinate with ordinary object-sortals and so that it presumes any arrangement of matter forms a unit, thereby assuming the very claim his argument intends to prove. I begin by reconstructing the argument from vagueness and assessing its two crucial denials: that there can neither be sharp cut-offs in composition, nor indeterminate cases of composition. I survey a variety of responses to these claims, which prove either unsatisfactory or ontologically burdensome, and offer my own response, which avoids ontological burdens. My strategy forces Sider into the dilemma of either recanting one of his two denials, or admitting that the fusions generated by his argument cannot bear ontological weight. Neither option can support a universal theory of composition. My purpose here is to refute the argument from vagueness; this paper does not advance a novel theory of composition. Nonetheless, the flaws I identify in Sider’s position advocate that an adequate theory of composition should countenance vague objects and attend to the distinct mereological nature of non-individuative physical substances, which requires further exploration.