Unlike English, which has almost completely lost the subjunctive it once had (especially in dialects spoken in the UK), Latin distinguishes it. Prototypically (i.e. most typically, in essence), the indicative expresses facts and the subjunctive expresses events that are or were hypothetical at some point. But then the language is seen allocating the subjunctive and the indicative to uses beyond these typical ones at seemingly random fashion. Latin, Spanish and French distinguish an indicative and subjunctive moods, but there's many differences between them on how they do it. For example, let's look at the typical subordinating conjunctions that mean 'after'. Spanish después (de) que
takes the subjunctive if it's a future action and the indicative if it's a past action (at least in the standard and in most dialects, any Argentinians in the forum are free to disagree). Latin postquam
typically takes the indicative, but now and then can be seen before a subjunctive (post accidisset quam dedissem, Cic. Ad Att.
VI.3). Many French speakers (especially editors) insist that après que
takes the indicative, but in spoken language it very
commonly takes the subjunctive instead.
Bottom line: I don't think you should try to find real "explanations" for uses of the indicative and subjunctive, but just learn them?
Maybe the plebeians would use the indicative and the patricians the subjunctive.
Considering that both the indicative and the subjunctive survived in about every Romance language (even Sardinian
, the one Romance language that got rid of almost all tenses), I'd disagree.