I want to defend a Combinatorialtheory of possibility. Such a view traces the very idea of possibility to the idea of the combinations – all the combinations which respect a certain simple form – of given, actual, elements. Combination is to be understood widely enough to cover the notions of expansion and contraction. The combinatorial idea is not new, of course. Wittgenstein gave a classical exposition of it in the Tractatus. Perhaps its charter is 3.4: ‘A proposition determines a place (...) in logical space. The existence of this logical place is guaranteed by the mere existence of the constituents’. There is a small additional combinatorial literature. I myself was converted to a combinatorial view by Brian Skyrms’ brief but fascinating article ‘Tractarian Nominalism.’. (shrink)