Breakdown of Luego, él los deja descansar profundamente.
él
he
descansar
to rest
luego
later
los
them (masculine direct object)
Questions & Answers about Luego, él los deja descansar profundamente.
Why do we use los instead of les before deja?
In causative structures like dejar + infinitive, the pronoun we use depends on the second verb. Because descansar (to rest) is an intransitive verb—meaning it doesn't take a direct object itself—the people resting become the direct object of the main verb deja. Therefore, we use the direct object pronoun los. If the infinitive had its own direct object (like letting them eat a meal), we would use the indirect object pronoun les instead.
Could we attach los to the end of descansar, like él deja descansarlos?
No, that sounds unnatural here. With causative verbs like hacer and dejar, the clitic pronoun almost always goes before the conjugated main verb (deja). The two verbs act as a single unit, so él los deja descansar is the standard and correct structure. Attaching the pronoun to the infinitive is generally reserved for other verb phrases like poder or querer.
I thought verbs of influence like letting or allowing triggered the subjunctive. Why does this use the infinitive descansar?
You can actually use either structure! Dejar and hacer are special because they frequently use the infinitive structure even when there is a change of subject (he lets, they rest). So, él los deja descansar is completely correct and very common. You could also use the subjunctive and say él deja que ellos descansen, but the infinitive is often preferred because it is much more direct.