El Imperfecto de Subjuntivo V perterito pluscuamperfecto de subjunctivo

Question

In your example of the

El Imperfecto de Subjuntivo

You're using the verb haber ie

Hubiera hubiese etc

So what's the preterito pluscuamperfecto de subjuntivo?

I thought that was

hubiera hubiese

I thought el imperfecto de subjuntivo was the past subjuntivo ie

Tuviera

Fuera

Pusiera

Etc

Answer

Hola Sandra,
El imperfecto de Subjuntivo of the verb haber is:
hubiera/hubiese
The same goes for tuviera/tuviese, quisiera, quisiese, pudiera/pudiese, hablara/hablase, etc...
What might be a bit confusing is that El Pluscuamperfecto de Subjuntivo of any verb is going to contain the forms hubiera or hubiese, because El Pluscuamperfecto is a perfect tense, therefore it's going to use haber + the participle of any verb, for example:

hubiera hablado
hubieses venido
hubieran cantado

In the lesson about the verb haber in El Imperfecto de Subjuntivo, you will only find sentences using hubiera/hubiese as an impersonal verb (there was/there were), not combined with any participle, because that would then be El pluscuamperfecto de Subjuntivo.
There is a TIP inside the lesson pointing out this difference. 
I hope this clarified it for you.
Saludos
Inma