An example of the contrast between realis and irrealis moods is seen in the English sentences "He works" and "It is necessary that he work". In the first sentence works
is a present indicative
(realis) form of the verb, and is used to make a direct assertion about the real world. In the second sentence work
is in the subjunctive mood
, which is an irrealis mood – here that he work does not necessarily express a fact about the real world (he could be rejecting necessity and refusing to work), but refers to what would be a desirable state of affairs.