Infinitivkonstruktionen: querer, poder und necesitar

Spanish builds "I want to eat", "I can swim", "I need to study" the way English does, with a conjugated verb followed by an infinitive. One difference makes life easier: there is no "to". The infinitive (hablar, comer, vivir) already contains it.

The first verb changes for the person, the second stays in the infinitive: Queremos ir a la playa. ¿Podéis venir el sábado? Mis padres prefieren cenar en casa.

No preposition in between

English "want to" tempts learners to add a little word: *Quiero a hablar, *Necesito de estudiar. These verbs take the infinitive directly. Other verbs do need a preposition, and those you learn as a set: ir a (voy a comer), empezar a, aprender a, tener que (tengo que trabajar - I have to work).

Saber or poder for "can"?

English "can" covers both, Spanish does not. Saber + infinitive is a skill you have learned: ¿Sabes conducir? - Can you drive? (do you know how). Poder is being able or allowed right now: Hoy no puedo conducir, he bebido una caña. - I can't drive today, I've had a beer.

Stem changes

Querer, poder and preferir change their stem vowel in the stressed forms: quiero, quieres, quiere, queremos, queréis, quieren; puedo, puedes, puede, podemos, podéis, pueden; prefiero. The nosotros and vosotros forms keep the original vowel because the stress moves to the ending.

Where the pronoun goes

An object pronoun can go before the conjugated verb or be attached to the end of the infinitive, with no change in meaning: Lo quiero comprar = Quiero comprarlo; ¿Me puedes ayudar? = ¿Puedes ayudarme? It cannot sit between the two verbs: *Quiero lo comprar.