 When we come to substantial facts, things are not so straightforward. A comparison with sets may be useful. There is a view according to which the existence of a set requires that of its members: in a world where, say, Socrates exists but not Plato, the set [Socrates, Plato] does not exist. And there is the more liberal view which says that every set exists necessarily. Corresponding to these two positions are the following two views about facts: