When to use the subjunctive in Spanish?

When to use the subjunctive?

In our introduction to the subjunctive, we said that fundamentally, the subjunctive is a special verb form that marks a non-assertion. A non-assertion is something like a "snapshot" of a situation without saying that it actually takes or took place— the rough equivalent of English phrases such as "Daniel coming", "for Mary to wait", that Bill should come back etc.

In practice, this "snapshotting" function means that the Spanish subjunctive ends up being used in a number of common types of construction:

to form the object of non-assertive verbs: that is, equivalents of English cases such as:

I want/asked (for) him to come
they proposed/suggested that he came (but he didn't)
Mary hopes for Daniel to get better
we prefer (for) the children to be safe
I'm angry that Jane was so late

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(in some cases) as the object of assertive verbs used in the negative (or which we might say are "intrinsically negative"). Note that in these cases, English doesn't generally use any special construction to mark 'non-assertiveness', but the underlined phrase would generally require a subjunctive in Spanish:

I don't think it's possible
I doubt he's capable

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in relative clauses, where the noun does not refer to a concrete thing or person:

I'm looking for a parrot that speaks Japanese
I don't know anybody who can help me

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in so-called impersonal constructions (it's possible/likely that...), which arguably fall into the following category;

to make a clause be the subject of the sentence: in fairly rare cases where a clause is made the subject of a sentence, that clause will generally have a subjunctive verb in Spanish. English tends to use either X -ing Y or for X to Y:

que lo haga es imposible
for him to do it is impossible
que venga mañana me queda mejor
him coming tomorrow suits me better

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In both Spanish and English, it's more common to put the clause after the verb; English requires a "filler" subject (generally "it"):

es imposible que lo haga
it's impossible for him to do it
me queda mejor que venga mañana
it suits me better for him to come tomorrow

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To form the imperative in many cases.

In certain time-related clauses, essentially where the time of the event in the subordinate clause occurs after the time frame of the main clause, including clauses meaning so that, in order that. Thus, the equivalents of the following would generally use a subjunctive in Spanish:

I'll do it when/before Juan gets back
I'll finish it now so that it's ready in time

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Similarly, when despues de ("after") introduces an event "in the future", it takes a subjunctive:

saldré despues de que llegue
I'll leave after he arrives-SUBJ

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Subjunctive in main clauses

A common feature of all the uses of the subjunctive mentioned above is that they occur in subordinate clauses (a "sentence within a sentence"). In a few cases, the verb in the main clause can occur in the subjunctive:

generally, the subjunctive is triggered by an adverb or phrase expressing "possibility", notably posiblemente, probablemente, quizás, talvez;

in such cases, the subjunctive is generally optional.