It would seem possible in principle … to reconstruct the ordinary sentential calculus in terms of phrastics only, and then apply it to indicatives and imperatives alike simply by adding the appropriate neustics.… It might be asked how we are to know, given two premisses in different moods, in what mood the conclusion is to be. The problem of the effect upon inferences of the moods of premisses and conclusion has been ignored by logicians who have not looked beyond the (...) indicative mood, … But if, as I do, we regard the entailment-relations of ordinary logic as relations between the phrastics of sentences, the problem becomes pressing. (R. M. Hare, The Language of Morals, pp. 26–28.). (shrink)

Anselm Müller; VIII*—Mental Teleology, Proceedings of the Aristotelian Society, Volume 92, Issue 1, 1 June 1992, Pages 161–184, https://doi.org/10.1093/aristote.