In this article we give a linguistic and a philosophical account of the relationship between some grammatical categories of the clause (realis) and the noun phrase (definiteness, specificity) that relate to the occurrence of an entity (thing, event) in the world of discourse. Our treatment differs in three important ways from previous work in this area. Firstly, we offer an explanation for both the symmetrical and the anti-symmetrical relations that appear to hold between (ir)realis mood and (in)definiteness. Secondly, we argue that any attempt to explain these relationships must make crucial reference to the grammatical category of specificity. Last but not least, we consider whether the identified linguistic symmetries and anti-symmetries are ontologically relevant and show that they are apparently best accounted for within an ontological theory that allows for dynamic and indeterminately located individuals.
