In trying to establish the view that there are no non-living macrophysical objects, Trenton Merricks has produced an influential argument—the Overdetermination Argument—against the causal efficacy of composite objects. A serious problem for the Overdetermination Argument is the ambiguity in the notion of overdetermination that is being employed, which is due to the fact that Merricks does not provide any theory of causation to support his claims. Once we adopt a plausible theory of causation, viz. interventionism, problems with the Overdetermination will (...) become evident. After laying out the Overdetermination Argument and examining one extant objection to it, I will explicate the relevant aspects of an interventionist theory of causation and provide a characterization of overdetermination that follows from such an account. From this, I will argue that the Causal Principle that undergirds the Overdetermination Argument is false and hence the argument is invalid; and I claim that the only other available characterization of overdetermination would render a key premise in the argument false. Thus, the Overdetermination Argument fails to provide us with any reason to deny the causal efficacy of macrophysical objects, and therefore provides no reason to doubt their existence. (shrink)