The Chunk: [Deber (conjugated)] + [infinitive]
Deber + infinitive expresses moral obligation or duty – what one ought to do. It's close in meaning to tener que, but with a stronger sense of moral weight.
You conjugate deber to match the person and then attach the infinitive of whatever action is required. No connector. No que. No de. Just verb + verb.
⚠️ Important: There is no que in this construction. It's "Debo estudiar" — never "Debo que estudiar." If you've seen the que form somewhere, that's a misunderstanding of Spanish grammar. This post teaches the real construction.
Why This Chunk Is Critical
- High frequency: You'll hear debo, debes, debemos + infinitive in conversation, writing, and formal speech constantly.
- Moral weight: Where tener que says "I have to," deber says "I ought to" or "I must" – a subtle but important difference.
- Low processing load: Once learned, it's a single retrieval – conjugate deber, add the infinitive.
Examples Across Different Subjects
Here's the chunk in action with all the key conjugations of deber:
Deber + Infinitive vs. Tener que + Infinitive vs. Deber de + Infinitive
Spanish has three related but distinct patterns with obligation and probability. Understanding the difference is essential:
Deber + infinitive — Moral obligation / duty
Debo estudiar. — I must study. (Moral weight, sense of duty.)
Tener que + infinitive — Practical necessity / task
Tengo que estudiar. — I have to study. (Practical, external obligation.)
Deber de + infinitive — Probability / supposition
Debe de estar cansado. — He must be tired. (A guess, not a duty.)
💡 Quick tip: Deber + inf = duty. Tener que + inf = task. Deber de + inf = probability. Don't mix them up!
Building Your Own Chunks
Once you know the pattern, plug in any infinitive to create a wide range of expressions:
Debo... — I must...
- Debo llamar a mi madre. — I must call my mother.
- Debo terminar esto hoy. — I must finish this today.
- Debo ser más cuidadoso. — I must be more careful.
Debes... — You must...
- Debes escuchar esto. — You must listen to this.
- Debes tener cuidado. — You must be careful.
- Debes respetar las reglas. — You must respect the rules.
Debemos... — We must...
- Debemos ayudarnos. — We must help each other.
- Debemos ser honestos. — We must be honest.
- Debemos resolver esto juntos. — We must solve this together.
Key Rules for This Chunk
- Deber is conjugated to match the person (yo → debo, tú → debes, etc.).
- No connector — no que, no de. The infinitive follows directly.
- The second verb is always in the infinitive — never conjugated.
✅ Debo estudiar. — I must study.
✅ Debemos comer. — We must eat.
❌ Debo que estudiar. — Non-existent construction. No que.
❌ Debo estudio. — Second verb is conjugated (should be estudiar).
Common Chunks with Deber
Here are some high-frequency chunks that use this pattern:
- Debo irme. — I must go (leave).
- Debes ver esto. — You must see this.
- Debemos hablar. — We must talk.
- Debe ser así. — It must be this way.
- ¿Debo hacer algo? — Must I do something?
Why This Matters for Your Fluency
Treating Deber + infinitive as a single chunk rather than assembling it from rules is exactly how native speakers use it. You'll hear this pattern often – in both Spain and Latin America – and once internalised, you'll use it naturally too.
🧠 Memory Tricks to Make Them Stick
-
🔵 Deber + inf = duty with weight — "Deber has the weight of duty"
Where tener que is "I have to," deber is "I ought to." More moral, less practical. -
🟡 Deber de = probability — "De + Deber = De + Probably"
The de adds doubt. Debe de estar = "He's probably there." Not obligation. -
🟢 No que, never que — "Deber never takes que"
Tener takes que. Deber doesn't. That's the key contrast. -
🔴 Debo / Debes / Debe — "Regular -er pattern, no surprises"
Unlike tener (irregular), deber is a regular -er verb. Easy conjugations.
Practice: Deber in Real Chunks
Everyday Chunks
- Debo llamar al médico. — I must call the doctor.
- Debes descansar más. — You must rest more.
- Debemos ahorrar dinero. — We must save money.
- Deben respetar las normas. — They must respect the rules.
Moral / Ethical Chunks
- Debemos ayudar a los demás. — We must help others.
- Debes decir la verdad. — You must tell the truth.
- Debo ser honesto conmigo mismo. — I must be honest with myself.
- Deben cumplir su palabra. — They must keep their word.
Everyday Phrases
- Debo irme ya. — I must go now.
- Debes probar esto. — You must try this.
- Debemos hablar seriamente. — We must talk seriously.
- Debo pensarlo mejor. — I must think it over.
Probability with Deber de (Contrast)
- Debe de estar cansado. — He must be tired. (Guess.)
- Deben de ser las tres. — It must be around three o'clock. (Estimate.)
- Debe de haber un error. — There must be a mistake. (Supposition.)
Key Takeaways
- Deber + infinitive = moral obligation / duty. No que, ever.
- Tener que + infinitive = practical necessity / task.
- Deber de + infinitive = probability, not obligation. Don't confuse them!
- Deber is regular — debo, debes, debe, debemos, debéis, deben.
- Moral weight: Deber is stronger and more moral than tener que.
- Both regions use it: Deber + infinitive is standard in Spain and Latin America alike.
🧠 Your Challenge
Step 1: Think of five things you feel you ought to do today – not just what you have to do, but what duty calls you to do.
Step 2: Say them out loud using "Debo..."
Step 3: Compare with tener que. Say each item both ways and notice the shift in feeling: "Tengo que llamar" (task) vs. "Debo llamar" (duty).
In just 30 seconds, you'll feel the subtle difference – and that's the mark of fluency.