Subjunctive with expression of feelings

Subjunctive with expression of feelings
 

It says that the subjunctive is used in the subordinate clause after certain expressions of feelings in the main clause, when there is a change of subject.

What does that mean?


For example: Me alegra que vengan mis amigos a nuestra fiesta

How is this applicable to the given use of the subjunctive?

The change of subject may be what you're confused about.

The use of the subjunctive mood in a subordinate clause is occasioned when the main verb expresses feelings, emotions, opinions, doubt and things that are contrary-to-fact, but only when there is a change in subject.

The subject is marked in green in these examples:

Espero poder ir a la fiesta.
= I hope I can go to the party.
(There's no change in subject, so no subordinate clause exists.)

Espero que puedas ir a la fiesta.
= I hope you can go to the party.
(The change in subject, from 'I' to 'you', mandates the use of a subordinate clause and, since the verb in the main clause is one that triggers the use of the subjunctive mood, the verb in the subordinate clause is cast in the subjunctive mood.)

Lamento no poder ir.
= I'm sorry I can't go.
Lamento que no puedan ir.
= I'm sorry you can't go.

Me alegra no haberlo visto.
= I'm glad I haven't seen it.
Me alegra que no lo hayan visto.
= I'm glad you haven't seen it.