 The metaphysical and ontological questions which are raised by the two views of facts mentioned include the following: Are the properties and relations which go to make up facts abstract (repeatable) universals or bearer-specific (non-repeatable) properties and relations (tropes)? If they are abstract universals, are these such that they are always exemplified, as friends of “Aristotelian” universals claim, or not, as friends of “Platonic” universals claim? And are they qualitative only (the property of being round) or also substantial (the property of being a man)? Are there facts containing abstract objects and properties, for example the fact that 2 is a number? Is a fact which contains a concrete object, for example the fact that Sam is sad, itself concrete or abstract? Are there facts which are formally complex, for example negative or conditional facts? What is the relation between facts, on the one hand, and concrete events, processes and states, on the other hand? Do objects stand in relations because the objects and the relations they stand in are parts of facts? What are the identity conditions for facts? Are there states of affairs which do not obtain? May such states of affairs contain non-existent objects? Are states of affairs abstract entities which exist necessarily? Do facts understood as exemplifications of properties come in two kinds—the contingently existing ones and the non-contingently existing ones? (For discussions of all these questions see the entry on  states of affairs.)  If concrete events, processes and states are identical with facts or can be constructed out of facts, then it is plausible to think that causality is a relation between facts. If they are not identical with facts and cannot be constructed out of facts, then it is plausible to think that causality is a relation between events and states and that causality should not be identified with causal explanations. For discussions of the view that one or both of the relata of the causal relation are facts, see Vendler 1967a,b; Menzies 1989; Mellor 1995; Persson 1997; and also the entry on  the metaphysics of causation.