[2005.] The subjunctive present is used in a protasis introduced by dum, until, when the main verb denotes either indefinite or present time, and the subjunctive imperfect when the main verb is past.
The subjunctive is an extension of the subjunctive of desire ([1540]); the clause denotes something expected or proposed.
is dum veniat sedens ibī̆ opperībere, Pl. B. 48, you shall sit there waiting till he comes. ōrandī sunt, ut sī quam habent ulcīscendī vim, differant in tempus aliud, dum dēfervēscat īra, TD. 4, 78, we must always ask such people, if they have any chance to take vengeance, to put it off to some other time, till their rage cool down. cēnseō latendum tantisper ibīdem, dum effervēscit haec grātulātiō et simul dum audiāmus, quemadmodum negōtium cōnfectum sit, Fam. 9, 2, 4, I advise lying low where you are, while the present congratulation excitement is cooling off, and at the same time till we may hear how the job was done. dum reliquae nāvēs eō convenīrent, in ancorīs exspectāvit, 4, 23, 4, he waited at anchor till the rest of the vessels should gather there ([1725]). Verginius dum collēgam cōnsuleret morātus, dictātōrem dīxit, L. 4, 21, 10, Verginius, after waiting till he should consult his colleague, appointed a dictator. observāvit dum dormitāret canēs, Pl. Tri. 170, he watched till the dog should be napping.
[2006.] The present indicative with dum, while, is sometimes used where the subjunctive might be expected with dum, until ([1593]). Other indicative tenses are rarely thus used: as,
([a.]) expectābō, dum venit, T. Eu. 206, I will wait while he comes. ego hīc tantisper, dum exīs, tē opperiar, Pl. Most. 683, I’ll wait for you here a while till you come out. ego in Arcānō opperior, dum ista cōgnōscō, Att. 10, 3, for myself I am waiting at the Arcae place, till I ascertain this. (b.) mihī̆ quidem usque cūrae erit, quid agās, dum quid ēgerīs, scierō, Fam. 12, 19, 3, for me I shall be anxious all the time to know what you are doing, till I know what you have done. mānsit in condiciōne usque ad eum fīnem dum iūdicēs rēiectī sunt, V. a. pr. 16, he stuck to his bargain till the jurors were challenged.
quoad, dōnec, until.
[2007.] quoad or dōnec, until, introduces a protasis in the present subjunctive when the main verb is present or future; and in the perfect indicative when the main verb is past or a general present.
quoad is found once in Plautus with the imperfect subjunctive ([2008]); in other authors here and there with both moods; not in Tacitus. With dōnec the present subjunctive is found once in Plautus, rarely in late Latin and in poetry; the perfect indicative is found at all periods; the present indicative ([1590]), found once in Plautus, is poetic and late. But dōnec is rarely used by Cicero, and never by Caesar or Sallust. dōnicum is found in old Latin (not in Terence) with the indicative ([2009]), and once in Nepos with the subjunctive of indirect discourse. dōnique is found four times in Lucretius with the indicative, always before vowels ([2009]). dōneque and dōneque cum seem to occur a few times in Vitruvius.
([a.]) ego hīc cōgitō commorārī, quoad mē reficiam, Fam. 7, 26, 2, I am thinking of staying here till I feel better. ea continēbis, quoad ipse tē videam, Att. 13, 21, 4, you will keep this back till I see you myself. expergēfactīque secuntur inānia saepe cervōrum simulācra, dōnec discussīs redeant errōribus ad sē, Lucr. 4, 995, and when awakened, often they still keep hunting the shadowy forms of stags, until the delusion is shaken off and they come to themselves. magnus mīrandusque cliēns sedet ad praetōria rēgis, dōnec Bīthȳnō libeat vigilāre tyrannō, J. 10, 160, a vassal great and strange he sits in the king’s gate, till it may suit his oriental majesty to wake. inter eadem pecora dēgunt, dōnec aetās sēparet ingenuōs, Ta. G. 20, they always live among the same flocks and herds, till maturity puts the free-born by themselves.