Russell's perspective on belief proved a point of contention between him and Wittgenstein, causing it to shift throughout his career. In logical atomism, belief is a complex that possesses both true and untrue propositions. Initially, Russell plotted belief as the special relationship between a subject and a complex proposition. Later, he amended this to say that belief lacks a proposition, and instead associates with universals and particulars directly. Here, the link between psychological experience – sense data – and components of logical atomism – universals and particulars – causes a breach in the typical logic of the theory; Russell's logical atomism is in some respects defined by the crossover of metaphysics and analytical philosophy, which characterizes the field of naturalized epistemology.