Confusion about subjunctive

Question

My old teacher used to insist that I write down every doubt I had Mi antiguo profesor insistía en que apuntara todas las dudas que tenía.In the correction given to me the answer was 'las dudas que tuviera'I see why apuntara is subjunctive but my doubt is 'tenía or tuviera' ?Gracias

Silvia Píriz · Accepted Answer

Hola David L.
You are right to question this, because both forms are possible in different contexts.
In your sentence:

Mi antiguo profesor insistía en que apuntara todas las dudas que tuviera.

both verbs after insistía en que are in the subjunctive:

apuntara → because insistir en que expresses insistence/request/influence

tuviera → because it refers to an indefinite or non-specific set of doubts

Here, las dudas que tuviera means something like “whatever doubts I might have” and “any doubts I had”.
So the speaker is not referring to a concrete, known set of doubts, but to any possible doubts. That is why the subjunctive sounds natural here.
Compare:
las dudas que tenía = the doubts I had (specific/real/identified doubts)
las dudas que tuviera = whatever doubts I might have / any doubts I had (non-specific)
So your original version with tenía is not grammatically impossible, but it changes the nuance slightly. In this context, native speakers would generally prefer tuviera because the sentence is talking about hypothetical or unspecified doubts in general.
Great question, this is one of those subtle uses of the imperfect subjunctive in relative clauses that often appears at C1 level.
Saludos
Silvia