As a follow on to these comments, I have gone through a retagged a bunch of questions about modality or mood. I have also suggested these tag wikis:
The grammatical category of modality includes realis/irrealis, epistemic, and deontic modality. If you want to ask about the subjunctive, optative, etc. morphological systems, then use the "mood" tag.
For questions about grammatical mood, such as the subjunctive, optative, imperative etc. To ask about realis/irrealis, epistemic, or deontic modality, use the "modality tag".
Questions on modal verbs (such as the English verbs can, might, must, should, etc.)
I think that this conveys the distinction usually seen between the grammatical categories of mood, and the semantic categories of modality. (The grammatical formally grammaticalising the semantic in some languages.) Further discussion on these tags is welcome!