Modal-like verbs: poder, deber, querer + infinitive

Puedo ayudarte.I can help you.

Spanish has three everyday verbs — poder, deber and querer — that go directly in front of an infinitive to talk about ability, obligation and desire. None of them need a preposition in between: the second verb just follows, unchanged.

Quick shortcut: poder = can/may, deber = should, querer = want to — all three + infinitive, no preposition.

poder + infinitive: ability and permission

Puedo ayudarte. (I can help you.) ¿Puedes venir mañana? (Can you come tomorrow?) No podemos entrar todavía. (We can't go in yet.)

Poder covers both physical/practical ability ("I'm able to") and permission ("I'm allowed to") — context usually makes clear which one is meant, the same way English can does. It's an o → ue stem-changing verb in the present (puedo, puedes, puede, podemos, podéis, pueden) — see stem-changing verbs for the full pattern.

deber + infinitive: obligation and advice

Debes estudiar más. (You should study more.) Deberíamos llamarla. (We should call her.) No debes mentir. (You shouldn't lie.)

Deber + infinitive expresses what someone should or ought to do — moral obligation, advice, a recommendation. It's a regular -er verb (debo, debes, debe, debemos, debéis, deben), no stem change.

deber de + infinitive: a guess, not an obligation

Adding de is meant to shift the meaning — from obligation to probability:

Debe de tener treinta años. (She must be about thirty.) Deben de estar en casa. (They're probably at home.)

In careful or formal usage, debe estudiar means "she should study" (obligation) and debe de estudiar means "she's probably studying" (a guess) — this is the recommended distinction, worth learning and aiming for. In everyday speech, though, plenty of speakers use deber alone for both meanings, and deber de sometimes shows up for obligation too — so hearing debe de estudiar meant as "she should study" isn't a sign something's ungrammatical, just that the speaker isn't keeping the two forms apart.

querer + infinitive: desire

Quiero aprender español. (I want to learn Spanish.) ¿Quieres comer algo? (Do you want to eat something?) No queremos esperar más. (We don't want to wait any longer.)

Querer is an e → ie stem-changing verb (quiero, quieres, quiere, queremos, queréis, quieren) — same family of change as poder, just a different vowel. Querer + infinitive is the everyday way to say what someone wants to do.

deber vs. tener que

Deber isn't the only way to talk about obligation — tener que + infinitive covers similar ground, with its own shade of meaning. Deber leans toward advice or moral obligation ("you should"); tener que leans toward a stronger, more concrete necessity ("you have to"). The two overlap heavily in everyday speech, and the difference is a topic of its own.

Common mistakes

• ❌ Puedo a ayudarte. → ✅ Puedo ayudarte. (no preposition between poder, deber, querer and the infinitive that follows.)
• Debe de estudiar más. (meant as advice, "she should study more") → clearer as ✅ Debe estudiar más. (in careful usage deber de signals a guess, not advice — keeping the two apart avoids the ambiguity, even though deber de for obligation is common in casual speech.)
• ❌ Quero aprender español. → ✅ Quiero aprender español. (querer is e → ie — the yo form is quiero, not quero.)

Quick check

1. Say "I can help you" using poder.
2. What's the difference in meaning between Debe llegar tarde and Debe de llegar tarde?
3. Give the tú form of querer in the present.
4. Correct this: Puedo a nadar muy bien.

Key takeaways

• Poder, deber and querer all go directly in front of an infinitive, no preposition.
• Poder = ability/permission (o → ue); querer = desire (e → ie); deber = obligation/advice (regular).
• Deber + infinitive = should/ought to; deber de + infinitive = probably, a guess — the recommended distinction, though many speakers blur it in casual speech.
• Tener que + infinitive also expresses obligation, with a stronger, more concrete feel than deber — its own topic.