Why is this in the subjunctive?

Question

I was recently given this sentence:

Eugenia (entender) ______ que no podamos ir.

I got it correct and know the form of "entender" to be used, but I have a side question: Why is "podamos" in the subjunctive here? Why not the indicative?

Answer

Hola Prahlad,

This is a classic construction which requires the subjuntivo.

There are two phrases "Eugenia understands" and "we are not able to go," linked by "que" and two different subjects - Eugenia and "we/us."

Espero que te ayude (I hope that [it/this] helps you) is exactly the same: Two phrases, Two different subjects "I" and "you," and "que" linking the two phrases.

Saludos. John

Answer

Hola Prahlad
I would justify here the subjunctive by saying that what is expressed in the relative clause (que no podamos ir) is something that is "known by the speakers", it is an "already shared information", therefore the subjunctive is used. So we have to assume somehow that they have already mentioned the fact that they can't go before in their conversation. 
It is very similar to what we explain with the "aunque" clauses (using the subjunctive for background information/known information/shared information).
Saludos
Inma

Answer

Prahlad - My grammar book (by Butt and Benjamin) points out that entender [and comprender] can sometimes contain undertones of emotion or personal sentiment - and adds that in those instances it is often appropriate to put the following verb in the subjunctive. In this particular case it probably implies that Eugenia also sympathises with our decision to not go.

Answer

True, I also think "entender" here implies an emotion, a feeling, therefore it falls into that category, together with others like:  me sorprende que..., me entristece que..., se alegra de que... etc