 It is certainly not easy to understand what would induce a compound to dissociate into its elements on Aristotle’s theory, which seems entirely geared to showing how a stable equilibrium results from mixing. The overwhelming kind of mixing process doesn’t seem to be applicable. How, for example, could it explain the separation of salt and water from sea water? But the problem for the advocates of the actual presence of elements is to characterize them in terms of properties exhibited in both isolated and combined states. The general problem of adequately meeting this challenge, either in defense of the potential presence or actual presence view, is the problem of mixture (Cooper 2004; Fine 1995, Wood &amp; Weisberg 2004).