Subjunctive with verbs of belief when asking a question....
 

My workbook on the subjunctive gives the following examples:

- Tú crees que la fiesta es hoy.
- Nosotros dudamos que la fiesta sea hoy.
- ¿Crees tú que la fiesta vaya a empezar pronto?

It goes on to say that "more traditional experts in style recommend that the subjunctive be used in subordinated clauses introduced even by verbs of belief - when asking a question."

What is the practice in common usage?

Using indicative or subjunctive implies ideas, only exceptionally style.

In your list of examples the last is the only one that admits both moods and some consideration about style is appropriate. The educated manner is trying to avoid any appearance of one looking for some specific answer if you really don't mean that, besides it is considered stylish to hide our own expectations and feelings. Some questions call for an affirmative answer by using indicative, some others call for a negative one by using subjunctive. The safest way is using subjunctive because you can safely communicate -by intonation and wording- that you are not expecting a negative answer.

¿Crees que la fiesta va a empezar pronto? (we don't know but it looks like we're expecting so)
¿Crees que la fiesta vaya a comenzar pronto? (we're not expecting so / we don't know and we'd like to)

Tú crees que la fiesta es hoy. (that's what you think ---> believed )
Tú no crees que la fiesta sea hoy. (that's what you think ---> not believed)
Tú no crees que la fiesta es hoy. (what you think opposes to what I know for sure)

Nosotros dudamos que la fiesta sea hoy
Nosotros no dudamos que la fiesta sea hoy
Nosotros no dudamos que la fiesta es hoy

What about, "Tú crees que la fiesta sea hoy?"

The difference between grammar and pragmatics. From a pragmatic point of view we might hear or say sentences like that. For instance, with the proper intonation it could mean "how come you believe such a thing!". But if the question is "¿crees que la fiesta sea hoy?" is just another polite manner to ask "¿crees que la fiesta es hoy?" and that is 100% grammatical.

To someone this may seem unnecessary or confusing but adding the pronoun or not is not a free option most of the times. It changes the meaning of the sentences. On the other hand, in some regional language, including areas of Spain and the state of New Mexico, even the affirmative sentence "tú crees que la fiesta sea hoy" may be grammatical with different values -I don't gather some of them yet- from a local point of view.

OK, sort of off-topic, but maybe not. Did you notice that you used a subjunctive in a subordinate clause there, in English? :)

Pragmatic, uh? :)

Anyway, thank you for the explanation.

You're welcome! :)

Lo entendí perfecto.

Al pan, pan, vino, vino. :)

:D

Saludos chileno:applause:

:)

Thank you Ma'am

Saludos para ti también.

Y bueno, para todos los que leen. :)