The subjunctive is just one of many historical aspects of English that are falling by the wayside. An example most people will recognize (and probably the only instance where the subjunctive would be commonly used) is saying "if I were" (subjunctive) rather than "if I was" (indicative).
Disclaimer: I prefer to use the subjunctive. I always use it where it is appropriate. It annoys me when people don't use the subjunctive. However, there is nothing "wrong" with using the indicative rather than the subjunctive. Many people did not acquire the use of the subjunctive when they acquired English. It is baseless and ridiculous to call the non-use of the subjunctive "improper English".
The subjunctive generally indicates situations that are counter-factual (contrary to fact, e.g., "I wish I were a millionaire"), conditional ("...whether it be/be it Communism, Capitalism, or some other economic structure..."), or, in certain rote phrases, future or nonaffirmative ("'til death do us part"). It was this last usage that caught me off guard, because I've never consciously analyzed that phrase, so familiar from wedding ceremonies. Upon reflection, I realized it must be the subjunctive (which in this case is signified by the bare form of the verb "do"), even though I can't think of a single productive instance (cf. *until he go to the store).
Bonus trivia: "If he were in the room" is counter-factual, and implies that he is not, while "If he be in the room" is a true conditional, implying that it is uncertain whether or not he is in the room (not that I've ever heard this used).
Jerome Stueart interview (pt. 3)
4 years ago