Often English grammar (as well as Koinê Greek, e.g "deponent", and probably others), has often been ruled by what I call "totalitarian grammarians" who impose Latin structures on it rather than doing a thorough internal study of the language; this is part of why the rules of classic English grammar can be so convoluted. (My father couldn't make any sense out of grammar in grade school but after studying linguistics is now a grammarian). Has English historically had a subjunctive, or is that an imposition of a Latin form upon the English construct that translates it? In other words, is there a more accurate description of what is often termed subjunctive in English?
Old English most certainly had a subjunctive. In fact, it had two, present and preterite, and they were inflected for person and number.
English now has three kinds of subjunctive (perhaps two, see below), the mandative, the formulaic and the were–subjunctive. The mandative is seen in sentences such as ‘I demand that he go.’ The formulaic appears in fixed expressions such as ‘come what may’, ‘heaven forbid’ and ‘suffice it to say’, while the were–subjunctive is an alternative to the indicative in clauses like ‘if I were you’.
The formulaic subjunctive is likely to be with us for as long as we used the fixed expressions that use it. The other two kinds are increasingly rare. The mandative subjunctive is probably found more in AmEng than in BrEng, which tends to favour the indicative or a construction with ‘should’. As Pam Peters says in 'The Cambridge Guide to English Usage’, ‘the motivation for using the were–subjunctive is stylistic rather than grammatical.' The authors of ‘The Cambridge Grammar of the English Language’ do not even regard it as subjunctive at all, describing it instead as ‘irrealis were’.