The Explanatory Role of Aggregate Properties

Forthcoming: C. K. Waters and J. Woodward (eds.), Causation and Explanation in Biology, volume 20 of Minnesota Studies in the Philosophy of Science. University of Minnesota Press, Minneapolis.

Abstract: An aggregate property, such as pressure, population, or concentration, is one whose realization is achieved by the joint instantiation of many more or less independent properties. This paper asks: can an aggregate property be causally relevant to a phenomenon if only some aspects of its realization play a direct role in causing that phenomenon, while the rest are, as it were, causal bystanders? I show that it is difficult for any known theory of causal relevance to distinguish aggregate properties that are genuinely causal from those that are not (such as conjunctions that bring together causally relevant properties and arbitrary, unrelated properties). I then develop a strategy for understanding the relevance of partially causal aggregates, diagnosing it as explanatory rather than strictly causal.