Should/Would Conditions or Future Less Vivid Conditions

The designation, "should/would conditions", offers a handy translation for most present subjunctive conditions in Latin. In fact, it is a better designation than the more common designation, "future less vivid condition." Consider the following sentence: "If a Martian should be sitting among us, he would wonder what we were up to." This is just an imaginary condition. The speaker is not concerned to say (what may seem obvious) that a Martian is not sitting among us. The speaker is only concerned with what would happen, and the speaker means what would happen today, right now, if a Martian were sitting here. In Latin, this is an open, imaginary condition. It takes the present subjunctive; it imagines the event as possible and as an open possibility. (In fact, Cicero says something very much like this at the beginning of his speech for Caelius.) On the other hand, if the speaker were concerned to make it clear that the Martian is in fact not among us now, the speaker would have to say, "If a Martian were sitting... among us (but he isn't), he would be wondering (but he isn't) what we were up to." So, you can see that the present subjunctive does not necessarily refer to the future: it imagines open potential.

It is also the case that the use of the present subjunctive has nothing to do with vividness. The category, "future less vivid," was invented because there were two kinds of conditions that typically referred to the future: conditions with the future indicative and conditions with the present subjunctive. Grammarians wondered what the difference was and guessed that difference between "If you will do this, I will fly" and "If a Martian should be here, he would be surprised." was one of vividness. It turns out that the difference really has to do with how the speaker is presenting the events: "If you do this, I will fly" is logical and factual (this kind of condition can be used rhetorically as a denial or as a threat, but we should not confuse rhetorical potential and use with the structure of syntactic difference); "If a Martian should be here... " is imaginary, potential, open.