Present subjunctive

The present subjunctive is a verb form used in certain constructions to express a "non-assertion". In simple terms, it is generally used in constructions that do not simply "state that something happens or will happen" (assertion). A clue to something being an assertion is that it can generally be contradicted using the formula no, ... doesn't/didn't. For example, in:

we could reply with either no, he didn't! or no, she didn't! to agree with either of the two assertions in the sentence. But in:

only the first of these contradictions, no, he didn't!, makes sense. This indicates that that Susan worked hard is not an assertion in this case. (Another feature of non-assertions in English is that that often cannot be omitted, whereas, for example, in sentence (1) it can.)

In Spanish, clauses that express a non-assertion-- such as that Susan worked hard in (2)-- generally have their verb in the subjunctive. Despite its name, the present subjunctive is generally the form used when this non-assertion is "non-past" rather than specifically "present".

Clauses introduced by cuándo (and a few other prepositions/conjunctions such as mientras) with a future reference, e.g. cuándo vengas = when you come; lo haré mientras trabajes = I'll do it while you're working;

In a construction that, in simple terms, "turns a noun phrase into a verb phrase". More precisely, this means where a clause is used in a position that would ordinarily be filled by a noun phrase (e.g. the subject or object of the verb, the complement of an adjective). For example:

Construction	When object is noun phrase	When object is clause (subjunctive verb)
quiero ...	quiero su ayuda ("I want his/her help")	quiero que me ayude ("I want him/her to help me")
contento de ...	contento de eso ("happy at that")	contento de que vengas ("happy that you're coming", "happy at you coming")

The imperative (command form). Negative imperatives are always based on the subjunctive, as are positive imperatives except for the tú form. For example: no comas! = don't eat!.

Typical constructions that don't trigger the subjunctive include verbs/expressions of simple 'saying or quoting' such as decir que ..., añadir que ..., es muy claro que ..., su declaración de que ... (his declaration that ...) etc.

A common but misleading perception is that the subjunctive is somehow a "learned" form, only used in "advanced constructions". In fact, subjunctive forms in Spanish are common, everyday forms used naturally in very frequent, ordinary constructions. For example, cuándo with a future time reference, or expressions such as no creo que... (I don't think that ...), are perfectly common in everyday speech (and generally trigger a subjunctive verb).

English equivalents to the subjunctive

English does not have subjunctive verb forms (although Old English did), and instead comparable constructions in English use other formulae such as:

As in sentence (2) above, English does not always have an obviously special construction to express a non-assertion. (Though as we mentioned, one special feature of (2) is that the word that is obligatory.) In cases such as (2), some dialects of English also use a so-called "null modal" construction (demanded that she work hard, in which she is followed directly by an infinitive, as though there is an "empty modal" verb between the two).

Formation of the Spanish subjunctive

Formation of the subjunctive is generally predictable if you know the present indicative (i.e. the "ordinary" present tense):

The present subjunctive of -ar has a similar form to the present indicative, but with a theme vowel of -e- instead of -a- (e.g. trabaje(s) instead of trabaja(s)).

Other verbs have a theme vowel of -a- (e.g. pueda(s) instead of puede(s)).

The first and third person singular forms (yo and él/ella) are always identical. So the 'theme vowel' of the subjunctive replaces the normal present tense -o ending: comer > (yo) coma.

For those few verbs with a 'special' first person singular present tense form (e.g. venir > vengo; decir > digo), then this special form is the basis for the entire present subjunctive: venga, vengas etc; diga, digas etc. All of these verbs have the -a- theme vowel in the present subjunctive (since none of them are -ar verbs).

Just a very small handful of verbs have irregular present subjunctive forms. See the conjugations of ser, ir haber, dar and estar.