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.

hunc audiēbant anteā; (Manil. 13), they used to hear of him before.
1. “[Sōcratēs] ita cēnsēbat itaque disseruit ” (Tusc. 1.72) , Socrates thought so (habitually), and so he spoke (then).
2. “prūdēns esse putābātur ” (Lael. 6) , he was (generally) thought wise. [The perfect would refer to some particular case, and not to a state of things.]
3. “iamque rubēscēbat Aurōra ” (Aen. 3.521) , and now the dawn was blushing.
4. “āra vetus stābat ” (Ov. M. 6.326) , an old altar stood there.

[*] Note.--The Imperfect is a descriptive tense and denotes an action conceived as in progress or a state of things as actually observed. Hence in many verbs it does not differ in meaning from the Perfect. Thus rēx erat and rēx fuit may often be used indifferently; but the former describes the condition while the latter only states it. The English is less exact in distinguishing these two modes of statement. Hence the Latin Imperfect is often translated by the English Preterite:—

1. “Haeduī graviter ferēbant, neque lēgātōs ad Caesarem mittere audēbant ” (B. G. 5.6) , the Hædui were displeased, and did not dare to send envoys to Cæsar. [Here the Imperfects describe the state of things.] But,—
2. id tulit factum graviter Indūtiomārus (id. 5.4), Indutiomarus was displeased at this action. [Here the Perfect merely states the fact.]
3. aedificia vīcōsque habēbant (id. 4.4), they had buildings and villages.