The present subjunctive in Spanish has many subleties and nuances but in most situations you can use it correctly following a few simple rules.
These rules and examples mostly relate to the present subjunctive in clauses introduced with que.
There are also examples of the imperfect subjunctive after que. This (in these examples) is used in the same way as the present, but when talking about past events.
Phrases making judgements such as it is doubful that/it is good that/it is untrue that etc are all followed by the present subjunctive, as are phrases expressing need.
|Es dudoso que ...||It is doubtful that ...|
|Es mentira que ...||It is untrue that ...|
|Es preciso que ...||It is essential that ...|
|Es conveniente que ...||It is useful that ...|
|Es natual que ...||It is natural that ...|
|Es importante que ...||It is important that ...|
|Es importante que veas||It is important (that) you see|
|Es necessario que ...||It is necessary that ...|
|Es necessario que lo hagas||It is necessary that you do it|
|Es obvio que ...||It is obvious ...|
|Es obvio que no sigues las instrucciones.||It is obvious that you don't follow instructions.|
Emotional reactions followed by que require the subjunctive.
|Me sorprende que...||It surprises me that...|
|Me sorprende que hubiera tantos ...||It surprises me that there were so many ...|
|Me asombra que...||It amazes me that...|
|Siento mucho que...||I'm sorry that...|
|Me preocupa que...||It worries me that...|
|Me irrita que...||It irritates me that...|
|Me irrita que lo hagas.||It irritates me that that you do it.|
|Ojala que...||If only .../Hopefully|
|Ojala que fuera||If only there were.|
Doubt, while not strictly an emotional reaction, also requires the subjunctive.
|Dudo que...||I doubt that...|
|Dudo que vayas.||I doubt (that) you (will) go|
Phrases where one person wants another to do something requires the subjunctive to be used.
|Quiero que...||I want ...|
|Quiero que me contestes||I want you to answer me.|
|Quiero que vayas||I want you to go|
|Deseo que...||I want/desire ...|
|Deseo que no digas tantas cosas||I don't want you to say such things|
|Necesito que...||I need ...|
|Prefiero que...||I prefer ...|
|Prefiere que su amiga no lo llame||He prefers that his friend does not call him.|
And in a negative sense
|No me gusta que...||I don't like (it that) ...|
|No me gusta que me hagas sentir como un bebé.||I don't like it when you make me feel like a baby.|
Often que has to be translated using 'when' in situations using the present subjunctive.
Denying the truth of a statement, fact or opinion.
|No creo que ...||I don't believe that ...|
|No creo que sea possible||I don't believe (that) it is possible|
|No creo que te den muchos||I don't believe (that) they will give you much|
|No parece que ...||It doesn't seem that ...|
|No es que ...||It isn't that ...|
|No es verdad que ...||It isn't true that ...|
|No pienso que ...||I don't think that ...|
|No pienso que esto sea correcto.||I don't think that is correct.|
If you are stating a fact, e.g. that someone doesn't believe something, then this isn't a denial and doesn't need the subjunctive. E.g. No crees que hay autobus.
Anytime you tell someone what to do or recommend a course of action (after que), use the subjunctive.
|Sugiero que ...||I recommend that ...|
|Prohibo que ...||I don't allow ...|
|Sugieres que lo hagamos?||Do you recommend/suggest that we do it?|
It is possible/probable that and so on.
|Es posible que ...||It is possible that ...|
|Es probable que ...||It is probable that ...|