  Because of the difficulty of the second problem it is useful to split it up into its own hierarchy by classifying statements in terms of their complexity. We shall discuss the hierarchy of statement complexity in more detail in the next section. But for the moment suffice it to say that (roughly speaking) one starts with questions of second-order arithmetic (stratified according to their complexity) and then one moves on to questions of third-order arithmetic (stratified according to their complexity), and so on. Thus, one first tries to solve the problem of selection at the level of, say, statements of second-order arithmetic and then one moves on to the problem of selection for statements of third-order arithmetic, and so on. The question of pluralism that we will be addressing is located in the hierarchy as follows: It takes a non-skeptical stance toward ZFC and seeks axioms that solve the problem of selection for the level of second-order arithmetic and somewhat  beyond.[2] 