In Old English, The subjunctive mood is a flexible grammatical instrument for expressing different gradients in thought when referring to events that are not stated as fact.
The word subjunctive as used to denote grammatical mood derives directly from the Latin modus subjunctivus.
In Indo-European, the optative mood was formed with a suffix *ieh or *ih (containing sounds as explained by laryngeal theory).
Already in Proto-Germanic (the distant ancestor of English, German, Dutch and Yiddish, as well as others), the optative became completely subsumed by the subjunctive.
From Proto-Germanic, the subjunctive mood passed down into the Ingvaeonic Anglo-Frisian group, also referred to as Insular Germanic, of which Old English is a member.
Not at all is [it] easy to escape – try as he might, he who will- The weak (I) verb “fremman” is rendered here in the third person singular present subjunctive.
Ġif messe-preost his áġen líf ríhtliċe fadie, þonne is ríht þæt his wurðscipe wexe.
Another use of the subjunctive in modern English is for noun clauses that follow certain types of verbs of command and desire.
In this usage the subjunctives convey that the noun clause is describing a state that is a possibility driven by a command or desire, yet not a present reality or future certainty.