[ Eighth Review, Lessons LXI-LXIX, §§ 527-528]
[ LESSON LXX]
THE CONSTRUCTIONS WITH THE CONJUNCTION CUM · THE ABLATIVE OF SPECIFICATION
[395.] The conjunction cum has the following meanings and constructions:
| cum temporal = when, followed by the indicative or the subjunctive cum causal = since, followed by the subjunctive cum concessive = although, followed by the subjunctive |
As you observe, the mood after cum is sometimes indicative and sometimes subjunctive. The reason for this will be made clear by a study of the following sentences:
1. Caesarem vīdī tum cum in Galliā eram, I saw Cæsar at the time when I was in Gaul.