(On the semantics and pragmatics of deontic should.)
I have a real-life example in mind here, from the NYT Magazine on the 17th, but I’m going to inch up to it, starting with these simpler examples:
(1) I should talk to my father.
(2) I should have talked to my father.
Both examples have the modal verb should, in its deontic sense, indicating obligation, duty, or correctness, incumbent upon some person, persons, or human institution; this is to be contrasted with its epistemic sense, indicating grounds for a judgment of truth — compare (1) and (2) with
(3) A sample this size should weigh about 10 kilograms.
(There are various ways to represent this difference, but that’s not my concern here.)
Then it turns out that deontic should can be used in (at least) two ways.