the Present Subjunctive in Noun Clauses

A noun clause is a group of words (containing a verb), which is the subject or object of the main clause verb:In the sentence "I demand that he be here", the words "that he be here" are the noun clause, object of the main verb "demand".

The subjunctive is used in a noun clause when the main verb expresses
influence (an indirect command), emotion, doubt, disbelief or denial.
Exijo que esté aquí. I demand that he be here.

• Spanish frequently uses the present subjunctive with a future meaning (the future subjunctive is no longer used):
Me alegra que haya clase mañana. I'm glad (that) there will be class tomorrow.
Note that the relative que cannot be ommitted as English often omits “that”.

A. INFLUENCE: After verbs expressing want, desire, hope, request, insistence, command, suggestion, etc., what is in the clause is like a command and must be in the subjunctive:

Espero que vayas. Te digo que lo hagas ahora. Insisto en que esté presente.

I expect you to go. Im telling you to do it now. I insist that he be present.

• English frequently uses a phrase with the infinitive to express indirect commands: "I want him to do it" etc. Spanish must use the subjunctive: Quiero que lo haga.

• If the verb in the main clause simply
reports a situation (usually with decir) perceived as real, use the indicative: Te digo que está lloviendo.I tell you that it is raining.

B. EMOTION: When the main verb expresses any
subjective attitudes (sorrow, surprise, anger, indifference, concern, hope), the verb in the noun clause must be in the
subjunctive:

Siento que no vayas. Me sorprende que Ud. no lo sepa. Es triste que no haga sol.

I am sorry that you're not going. It surprises me that you do not know it. It's sad it isn't sunny.

• With verbs of influence and emotion, use the infinitive if there is only one subject::

Quiero ir. Espero ir. Siento molestarte. Estamos felices de trabajar aquí.	I want to go. I hope to go. I'm sorry to disturb you. We're glad we work here.
BUT: Estamos felices de que trabajes aquí.	We're glad that you work here.

C. DOUBT, DISBELIEF or DENIAL: When the main verb expresses uncertainty or denies a previous statement, the verb in the noun clause should be in the subjunctive:

Doubt or Disbelief:	Dudo/No creo que vaya. No es posible que sea verdad. Es increíble que te vayas.	I doubt/I don't think I'm going. It's not possible that it is true. It's hard to believe you're leaving.
Denial:	No digo que sea tonto. Es falso que me moleste el ruido. No es cierto que haya marcianos.	I am not saying (that) he is stupid. It is false that noise disturbs me. It's not true that there are Martians.

• In general, creer, no dudar, ser verdad, and other expressions of conviction are not followed by the subjunctive, while no creer, dudar, no ser cierto, etc., are:
Creo que va a llover but No creo que llueva
In questions, the clause may not involve a subjunctive, depending on the doubt in the mind of the speaker:
¿Crees que va a llover? or ¿Crees que llueva?

Ojalá, whose form is invariable, meant originally something like "O to Allah" in Arabic and it is used to express a general wish or hope. It is always followed by the subjunctive:

Ojalá (que) vengan mañana. Ojalá no llueva.

I hope they come tomorrow. Hopefully it won't rain.

Ojalá may be used with or without que with no change in meaning.
See www.colby.edu/~bknelson/SLC/ojala/cancion.html for a good practice on ojalá in a Dominican song.

 tal vez, quizás, quizá, which all mean perhaps, are followed by the subjunctive if the speaker wants to convey a considerable degree of doubt (que is not used here):

Tal vez llegue pronto. Quizás vamos al cine.

Perhaps he will arrive soon. (probably not) Maybe we'll go to the movies. (very possible)

Más ejercicios y la página original en el enlace.