Allen and Greenough's New Latin Grammar for Schools and Colleges
J. B. Greenough, G. L. Kittredge, A. A. Howard, Benj. L. D'Ooge, Ed.

In translating, the English Imperfect must generally be used:—

1. “ dum haec geruntur, Caesarī nūntiātum est ” (B. G. 1.46) , while this was going on, a message was brought to Cæsar.
2. “haec dum aguntur, intereā Cleomenēs iam ad Elōrī lītus pervēnerat ” (Verr. 5.91) , while this was going on, Cleomenes meanwhile had come down to the coast at Elorum.
hōc dum nārrat, forte audīvī; (Ter. Haut. 272), I happened to hear this while she was telling it.

[*] Note.--This construction is a special use of the Historical Present (§ 469).

[*] a. A past tense with dum (usually so long as) makes the time emphatic by contrast; but a few irregular cases of dum with a past tense occur where no contrast is intended:

1. “nec enim dum eram vōbīscum, animum meum vidēbātis ” (Cat. M. 79) , for while I was with you, you could not see my soul. [Here the time when he was alive is contrasted with that after his death.]
2. “coörta est pūgna, pār dum cōnstābant ōrdinēs ” (Liv. 22.47) , a conflict began, well matched as long as the ranks stood firm.
3. But,—dum oculōs hostium certāmen āverterat (id. 32.24), while the struggle kept the eyes of the enemy turned away.
4. “ dum ūnum adscendere gradum cōnātus est, vēnit in perīculum ” (Mur. 55) , while he attempted to climb one step [in rank] he fell into danger.

[*] Note.--In later writers, dum sometimes takes the Subjunctive when the classical usage would require the Indicative, and dōnec, until, is freely used in this manner (especially by Tacitus):—

1. “ dum ea in Samniō gererentur, in Etruriā interim bellum ingēns concītur ” (Liv. 10.18) , while this was being done in Samnium, meanwhile a great war was stirred up in Etruria.
2. “illa quidem dum tē fugeret, hydrum nōn vīdit ” (Georg. 4.457) , while she was fleeing from you she did not see the serpent.
3. “ dum per vīcōs dēportārētur, condormiēbat ” (Suet. Aug. 78) , while he was being carried through the streets he used to fall dead asleep.
4. Rhēnus servat nōmen et violentiam cursūs (quā Germāniam praevehitur) “ dōnec Ōceanō misceātur” (Tac. Ann. 2.6) , the Rhine keeps its name and rapid course (where it borders Germany) until it mingles with the ocean.
5. temporibusque Augustī dīcendīs nōn dēfuēre decōra ingenia dōnec glīscente adūlātiōne dēterrērentur (id. 1.1), for describing the times of Augustus there was no lack of talent until it was frightened away by the increasing servility of the age.

For dum, provided that, see § 528.