While the English language lacks distinct inflections for mood, an English subjunctive is recognized in most grammars. Definition and scope of the concept vary widely across the literature, but it is generally associated with the description of something other than apparent reality. Traditionally, the term is applied loosely to cases in which one might expect a subjunctive form in related languages, especially Old English and Latin. This includes conditional clauses, wishes, and reported speech. Modern descriptive grammars limit the term to cases in which some grammatical marking can be observed, nevertheless coming to varying definitions.

In particular, The Cambridge Grammar of the English Language narrows the definition further so that the usage of were, as in "I wish she were here", traditionally known as the "past subjunctive", is instead called irrealis. According to this narrow definition, the subjunctive is a grammatical construction recognizable by its use of the bare form of a verb in a finite clause that describes a non-actual scenario. For instance, "It's essential that he be here" uses the subjunctive mood while "It's essential that he is here" does not.