Haya vs hubiera

Question

Nos extrañó que ustedes hubiesendecidido mudarse.We found it odd that you had decided to move.Would  hayan decidido be incorrect here? The difference between hayan and hubieran in the absence of a conditional state that remains unclear.

Inma Sánchez · Accepted Answer

Hola Jeffrey
The  use of the preterite tense in the main clause triggers the pluperfect subjunctive in the subordinate clause. This is a natural sequence of tenses. The use of the perfect subjunctive (hayan decidido) would be justified with the main clause using the present or the present perfect:

Me extraña que hayan decidido mudarse.
 
I find it odd that they have decided to move.
Me ha extrañado que hayan decidido mudarse. 
I found it/have found it odd that they have decided to move.

With the preterite in the main clause in Spanish you can say:

Me extrañó que decidieran mudarse. 
I found it odd that they decided to move.

or

Me extrañó que hubieran decidido mudarse.
I found it odd that they had decided to move.

I hope this clarified it.
Saludos
Inma