  Emergent Modalities.   Combinatorialism purports to  explain a further class of intuitive modal facts as features that  simply “emerge” from facts about structural   properties.[55]  The discussion of structural states of affairs and supervenience  above provides an example. Let us suppose the actual world  w1 includes our water molecule W from Figure 1 plus a further hydrogen atom h3. In this world,  only h1 and h2 bind to o.  Hence, this world includes the state of affairs W's being  water but not the state of affairs I's being hydronium in  which o, h1, h2, and  h3 are so bonded as to constitute a hydronium ion  I. Conversely, however, given the unrestricted nature of  recombination, there is a world w2 that includes  W structured as it actually is in w1 but  which also includes the spoiler  [B,o,h3] — where o and  h3 bond — and, hence, the structural state of affairs I's being hydronium. Thus, the absence of  [B,o,h3] in w1  enables the emergence of W's being water and precludes I's  being hydronium whilst its presence in w2  enables the emergence of the latter but precludes the former. As a  consequence, it is impossible that the states of affairs W's  being water and I's being hydronium   coexist.[56] 