   In the abstract, there are two sorts of arguments Russell could have given for the existence of simples, a priori arguments, or empirical arguments (cf. Pears 1985, 4ff). An a priori argument might proceed from the very understanding of complexity: what is complex presupposes parts. In 1924, Russell wrote, “I confess it seems obvious to me (as it did Leibniz) that what is complex must be composed of simples, though the number of constituents may be infinite” (LA, 337). However, if construed as an argument, this does not seem very convincing. It seems at least logically possible that while a complex may have parts, its parts might themselves be complex, and their parts might also be complex, and so on, ad infinitum.  Indeed, Russell himself later came to admit that one could not know simply on the basis of something being complex that it must be composed of simples (MPD, 123).