In English, the subjunctive mood is used to explore conditional or imaginary situations. It can be tricky to use, which partially explains why many speakers and writers forgo it. But it’s quite useful (and aesthetically pleasing, at least to us), and careful users of English should do their part to preserve it.
Uses of the subjunctive mood
The subjunctive mood is used to explore conditions that are contrary to fact:
If I were President, I wouldn’t put up with it. [National Review]
It’s used to explore hypotheticals:
If I were to embroider a sampler, it would say, “Simple is truly best in Frytown.” [Z Wire]
It’s used to express wishes:
I wish I were there to have a drink with you and dish. [Ebar]
It’s used to express commands or demands:
She demanded that he leave the hospital premises … [Salem News]
It’s used to express suggestions:
I suggest that he implement a budget cut in March. [Daily Gleaner]
It’s used to make statements of necessity:
It’s essential that they be heard … [Alternet]
Subjunctive mood and verb tense
Since statements in the subjunctive mood exist outside time, tense applies differently. In the last four subjunctive mood examples above, the tenses of the indicative verbs (wish, demanded, suggest, is) could change, and the subjunctive verb indicating the imagined action (were, leave, implement, be) would not change—for example:
I wished I were there to have a drink with you and dish.
She will demand that he leave the hospital premises.
I suggested that he implement a budget cut in March.
It will be essential that they be heard.
With subjunctive if constructions, things get trickier. In these statements, there is no concrete action, so there is no real tense. However, we still categorize them in terms of when the imagined action would take place. For instance, the first of the above subjunctive mood examples is in the present subjunctive. The future subjunctive would look like this:
If I were to become President in 20 years, I wouldn’t put up with it.
Of course, this begins to stretch the subjunctive mood beyond necessity, which is why the future subjunctive is rarely used. In this case, it would be much easier to use the indicative mood:
If I become President in 20 years, I won’t put up with it.
In the past subjunctive mood, the verb tense of the imagined action does change—for example:
If I had been President, I wouldn’t have put up with it.
If you’re confused by the subjunctive mood, don’t worry too much. As with all grammar and usage matters, the rules for subjunctive mood are based on centuries of convention. There’s no deeper reason; it just is what it is. But the subjunctive mood is useful, and it would be a shame if it were to go away.