 Although the grounds of possibility and intentionality were prominent themes in the modern  period,[9]  the idea of explaining them in terms of any sort of bifurcation of being largely receded until the early nineteenth century beginning, notably, with the remarkable work of  Bernard Bolzano.  Specifically, in his work on the ground of possibility, Bolzano developed a sophisticated bi-modal account of being on which everything there is divides into those things (Dinge) with Wirklichkeit, usually rendered “actuality” by Bolzano’s  translators,[10]  and those with Bestand, typically rendered “subsistence”. Importantly, for Bolzano as well as for many of his successors, to be actual (wirklich) is to be part of the causal order and, hence, typically at any rate, to occupy a position in space and time—in a word (as commonly understood), to be  concrete.[11]  Subsistence, by contrast, is the mode of being shared by non-concrete objects, which in particular for Bolzano included both possibilia and abstracta like numbers and propositions. Unlike abstracta, however, Bolzano’s possibilia are only contingently subsistent, contingently non-concrete, and, hence, are capable of Wirklichkeit: