A specificational clause is an °equational clause in which the °topic is a °variable nominal and the °comment is a °value nominal.
An example is "The capital of Poland is Warsaw". Specificational clauses contrast with characterizational clauses, where the topic is a value nominal and the comment is a variable nominal (e.g. "Warsaw is the capital of Poland"); see Haspelmath (2025: §9). The term "specificational" appears to go back to Higgins (1973). ❡
Croft's "identificational" is similar, using a notion of "presupposed open presupposition" for the notion of "variable" used here.
identificational (INF/CXN) = information packaging in which a particular piece of information (the focus) is equated with the “open slot” in a presupposed open proposition; and the construction that expresses that information packaging. The presupposed open proposition may be evoked by an alternative proposition that differs from the identificational construction by only the focus. Example: in It was Ollie who was play- ing the piano, the information in the identificational construction is divided into the presupposed open proposition ‘X was playing the piano,’ and the focused information Ollie, and what is being asserted is ‘X = Ollie.’ The term ‘focus’ is sometimes used as a synonym for ‘identificational,’ but this term is used differently here. (Sections 10.1.2, 11.1, 11.4.1)