How would I say "as long as"?

Question

Suppose I want to write about Meleager, fated to live exactly as long as a certain branch of wood lasts (no longer, no shorter). Or perhaps I'm writing about Cincinnatus, who agreed to hold power as long as Rome was threatened, but then to go back to his farm afterward.

How would I express the phrase as long as in Latin? The meaning is fairly similar to "while" in English, but cum with a subjunctive doesn't feel emphatic enough for something like Meleager's prophesied lifespan.

Answer 1

For both your examples, you could use quamdiu (also written quam diu) with an indicative verb, either with or without the correlative tamdiu/tam diu, as in Cicero, Ad familiares 12.19.2:

quod si paris copias ad confligendum non habebis, non te fugiet uti consilio M. Bibuli, qui se oppido munitissimo et copiosissimo tam diu tenuit quam diu in provincia Parthi fuerunt.

But if you have not forces adequate for the struggle, do not forget to follow the policy of M. Bibulus, who kept himself shut up in a very strongly fortified and well-supplied town, as long as the Parthians were in the province.

(Translated by Evelyn Shuckburgh)

Other options are quoad, donec, and even dum, when the clauses containing these words have an indicative verb – for example:

• Livy, Ab urbe condita 26.51.5:

  hunc ordinem laboris quietisque quoad Carthagine morati sunt servarunt.

  They preserved this pattern of work and rest as long as they lingered in Carthage.

• Tacitus, Historiae 4.12:

  Batavi, donec trans Rhenum agebant, pars Chattorum, seditione domestica pulsi extrema Gallicae orae vacua cultoribus simulque insulam iuxta sitam occupavere, quam mare Oceanus a fronte, Rhenus amnis tergum ac latera circumluit.

  The Batavians, so long as they lived beyond the Rhine, formed a branch of the Chatti. Drven out by domestic dissensions, they occupied the uninhabited riverine fringes of Gaul together with the 'Island' in the lower reaches, washed by the North Sea on the west, and on the other three sides by the Rhine.

  (Translated by Kenneth Wellesley)

• Cicero, Pro Roscio Amerino 126:

  dum praesidia ulla fuerunt, in Sullae praesidiis fuit; postea quam ab armis <omnes> recesserunt, in summo otio rediens a cena Romae occisus est.

  For as long as there were any garrisons, he was in the garrisons of Sulla; after everyone put down arms, he was killed in Rome as he was returning from dinner in the utmost leisure.

See, e.g, Allen and Greenough, New Latin Grammar §552ff.

Answer 2

Another option is dum. Lewis & Short (i.q. = idem quod):

... B. With respect to the temporal limit of both actions, i. q. tamdiu quam or usque eo, as long as, while.

1. Lit. (with indic. when the duration of the action in the principal clause is alone implied, except in the oratio obliqua).—In praes.: bene factum a vobis, dum vivitis, non abscedet, Cato ap. Gell. 16, 1 fin.; so Cic. Lael. 4, 14; id. de Sen. 23, 86; id. Fin. 3, 2, 9; Caes. B. G. 7, 50 fin. al.—In fut.: quid illos opinamini animi habuisse atque habituros, dum vivent? Cato ap. Gell. 10, 13, 17; Plaut. Ps. 1, 3, 103; Cic. Rosc. Am. 32 fin.; id. Leg. 1, 1, 2; Verg. A. 1, 607 sq. et saep.—

(b). Subj., often, when the clause with dum expresses a desired end, or refers to an indefinite future: "non tibi venit in mentem, Si, dum vivas, tibi bene facias, etc.", Plaut. Bacch. 5, 2, 76: "pars, dum vires suppeterent, eruptionem censebant", Caes. B. G. 7, 77, 2: "ut sua sponte, dum sine periculo liceret, excederet Gadibus", id. B. C. 2, 20, 3: "hoc unum esse tempus de pace agendi, dum sibi uterque confideret ut pares ambo viderentur", id. ib. 3, 10, 7: "de quo (sc. animo) dum disputarem, tuam mihi dari vellem, Cotta, eloquentiam", Cic. N. D. 2, 59, 147 Bait. (v. Roby, Gram. 2, 284 sq.). —

b. With tamdiu, tantum, tantummodo, tantisper, usque; or opp. postea, postquam, deinde, ubi, nunc, etc.—With tamdiu, Cic. Verr. 2, 4, 3; id. Cat. 3, 7; id. de Sen. 12, 41; id. Tusc. 5, 33 fin.; id. Att. 9, 6, 5 al.—With tantum, Liv. 27, 42.—With tantummodo, Sall. J. 53, 3.—With tantisper, Plaut. Truc. prol. 11; Ter. Ad. 1, 1, 44; id. Heaut. 1, 1, 54.—With usque, Cic. Verr. 2, 1, 5: dum ... postea, id. Mur. 12, 26—dum ... postea quam, Caes. B. G. 7, 82, 1; Cic. Rosc. Am. 43 fin.—dum ... postquam, Sall. J. 53, 3; Liv. 21, 13; cf. Ter. And. 1, 1, 27—dum ... deinde, Cic. Att. 9, 6, 5; Liv. 27, 42, 13—dum ... sed ubi, Plaut. Capt. 2, 1, 37; Caes. B. C. 1, 51, 5—dum ... nunc, Ter. And. 1, 2, 17; Cic. Ac. 1, 4, 11.—For tamdiu ... dum, less freq. dum ... dum, as long as ... so long: "sic virgo dum intacta manet, dum cara suis", Cat. 62, 45 and 56; cf. Quint. 9, 3, 16: "dum habeat, dum amet", Plaut. Truc. 2, 1, 23 (al. tum).—

c. In Plautus repeatedly with an emphatic quidem, Plaut. As. 2, 4, 57; 5, 2, 20; id. Bacch. 2, 2, 48; id. Merc. 2, 3, 53; id. Ps. 1, 5, 92.— ...