Breakdown of No creí que él hubiera entendido su propia capacidad.
él
he
no
no, not
su
his/her/its/their/your (formal)
entender
to understand
Questions & Answers about No creí que él hubiera entendido su propia capacidad.
Why use the past perfect subjunctive (hubiera entendido) instead of the imperfect subjunctive (entendiera)?
It is about the timeline. The main verb No creí is in the past, and the understanding happened even earlier than that past belief. Because it is a past action that occurred before another past action, we need a perfect tense ('had understood'). Since it is triggered by a negative belief (No creí que...), it must be in the subjunctive mood.
Would I still use the subjunctive if the sentence were affirmative, like 'I believed that he had understood'?
No. Affirmative belief verbs like creer or pensar declare what the speaker considers to be a fact, so they trigger the indicative mood. If you said 'I believed,' it would be Creí que él había entendido. We only use the subjunctive here because the belief is negative (No creí), which introduces doubt into the dependent clause.
Why do we need the word propia here? Doesn't su already mean 'his'?
Is it possible to use hubiese instead of hubiera in this sentence?