In grammar, the subjunctive mood (abbreviated sjv or sbjv) is a verb mood typically used in subordinate clauses to express various states of unreality such as wish, emotion, possibility, judgment, opinion, necessity, or action that has not yet occurred. It is sometimes referred to as the conjunctive mood, as it often follows a conjunction. The details of subjunctive use vary from language to language.

The reconstructed Proto Indo-European language is the putative parent of many language families. These include the Romance languages, Celtic languages, Germanic languages (including English), the Greek language, Slavic languages, many of the languages of the Indian subcontinent and the Iranian or Persian languages and several others. It had two closely related moods: the subjunctive and the optative. Many of its daughter languages combined or merged these moods. In Indo-European, the subjunctive was formed by using the full ablaut grade of the root of the verb, and appending the thematic vowel *-e- or *-o- to the root stem, with the full, primary set of personal inflections. The subjunctive was the Indo-European irrealis, used for hypothetical or counterfactual situations. The optative mood was formed with a suffix *-ieh1 or *-ih1 (with a laryngeal). The optative used the clitic set of secondary personal inflections. The optative was used to express wishes or hopes. Among the Indo-European languages, only Albanian, Avestan, Ancient Greek, Sanskrit, and to some extent Old Church Slavonic kept the subjunctive and optative fully separate and parallel. However, in Sanskrit, use of the subjunctive is only found in the Vedic language of the earliest times, and the optative and imperative comparatively less commonly used. In the later language (from c.500BC), the subjunctive fell out of use, with the optative or imperative being used instead, or merged with the optative as in Latin. However, the first person forms of the subjunctive continue to be used, as they are transferred to the imperative, which formerly, like Greek, had no first person forms. [edit]Germanic languages In the Germanic languages, subjunctives are also usually formed from old optatives. In German, subjunctives are typically marked with an -e ending, and often with i-umlaut, showing once more the presence of the *-i- suffix that is the mark of the old optative. In Old Norse, an -i is involved in many subjunctive constructions; grefr, "he digs", becomes grafi, "let him dig"; and an i-umlaut occurs in subjunctive derivations in the strong verbs.[1] Below are two tables showing the Old Norse active paradigm of the verb grafa (“to dig”):