Chief uses of the subjunctive

some exx. from Ovid Metamorph. 1.357-64; add exx. from Livy

(A) Purpose, Result, etc. with ut, ne or ut non (for result)

(1) Result often follows tantus (etc.), ‘so much/great’ ... that:

tanta opibus Etruria erat ut iam non terras solum sed mare etiam

... fama nominis sui implesset

(2) Purpose should be self-evident:

Jupiter sends clouds so that man may be destroyed" Jupiter nubes mittit ut viri deleantur. 

Present main verb takes present subjunctive, but past main verb takes imperfect subjunctive

 --> Jupiter nubes misit ut viri delerentur.

(3) Like purpose clauses are clauses of fearing with ne (=lest/that):

Jupiter feared that heaven would catch fire ...

Sed timuit ne aether / conciperet flammas longusque ardesceret axis

(B) The most versatile uses are

          (1) Indirect question.

You ask what he is doing (present) ——>  Rogas quid faciat.

    "    what he has done         (perfect)  ——>  Rogas quid fecerit

   "     what is being done (pres.pass.)—>           Rogas quid faciatur

   "     what has been done (perf. pass.)—>        Rogas quid factum sit

Remember, after past-tense main verb, subjunctives must all be past:

You asked (past) what he did/was doing (then)—> Rogavisti quid faceret

          "        what he had done (pluperf) ——> Rogavisti quid fecisset

          "        what was being done (passive) —> Rogavisti quid faceretur

          "        what had been done (plupf. pass.)—> Rogavisti quid factum esset

          (2)  Cum circumstantial clauses: 

While/since the Trojans were plundering the fields (Liv. 1.1)

          --cum praedam ex agris agerent—Latinus attacked.

Although he could fend off the attack from the walls, he led out the troops ... 

(Liv. 1.2), cum moenibus bellum propulsare posset,  in aciem copias eduxit

          (3) Relative (qui) clause of characteristic (often causal with ut)

... (like men) for whom nothing remained but weapons and ships

(ut) quibus ... nihil praeter arma et naues superesset

(C) Dependent clause in indirect statement, esp. temporal clauses

(that would be indicative in oratio recta)

When the battle lines were drawn, before they gave the signal, ...(Liv. 1.1. 7-8)

cum instructae acies constitissent, priusquam signa canerent processisse Latinum

after he heard (they were Trojans, etc.), postquam audierit ...

(D) Conditions (if/then), esp. Contrary to Fact:

(1) Oddly, "present contrary-to-fact" uses imperfect subjunctive and is

          translated with "should/would/were to:"

 If the sea should/were to destroy mankind, the gods would receive no sacrifices

—— Si pontus viros deleret, dei nulla sacra caperent

(2) "past contrary-to-fact" uses pluperfect subjunctive and is

          translated "had/would have"

If the sea had destroyed mankind, the gods would have received no sacrifices

——> Si pontus viros delevisset,  dei nulla sacra cepissent.

(E) And subjunctives are occassionally used as main verbs

          (1) to express a wish (esp. impf.),  often with ut or utinam, translated "would that ...may/might/were/had"

Would that the gods might save mankind! —> utinam dei viros servarent

would that the gods had saved mankind (they didn't)

          —> utinam dei viros servavissent

          (2) to express potential or possibility, ‘could/might’

quis enim rem tam veterem pro certo adfirmet?

‘Who could confirm for certain...’ (Liv. 1.3)