Breakdown of Dudé que ellos hubieran usado el conocimiento.
ellos
they
usar
to use / to wear
que
that / than
haber
(auxiliary) have
Questions & Answers about Dudé que ellos hubieran usado el conocimiento.
Why do we use the past perfect subjunctive (hubieran usado) here instead of the imperfect subjunctive (usaran)?
The main verb dudé is in the past tense and expresses doubt, which triggers the subjunctive. We use the past perfect subjunctive (hubieran usado) to show that the action of using the knowledge happened before the moment of doubting. If you used the imperfect subjunctive (usaran), it would mean "I doubted that they were using it" (happening at the exact same time as the doubt).
Could I say "hubiesen usado" instead of "hubieran usado"?
Yes, absolutely! The imperfect subjunctive of haber has two valid endings: the -ra form (hubieran) and the -se form (hubiesen). They are completely interchangeable in meaning, though the -ra form is much more common in everyday Latin American speech.
Since "dudé" triggers the subjunctive, what happens if I say "I didn't doubt"?
If you change it to no dudé (I didn't doubt), you are now expressing certainty rather than doubt. Certainty triggers the normal indicative mood. So, the sentence would change to use the past perfect indicative instead: No dudé que ellos habían usado el conocimiento.
Why is the article "el" used before "conocimiento"?