Modal Verbs: können, müssen in German

Overview

Modal verbs are special verbs that express ability, necessity, permission, or obligation. At the A1 level, the two most important ones are können (can, to be able to) and müssen (must, to have to). These verbs work differently from regular verbs because they pair with a second verb in its infinitive form, which goes to the end of the sentence.

The sentence structure changes when you use a modal verb: the modal verb is conjugated and sits in Position 2 (as usual), while the main verb stays in its infinitive form and moves to the very end of the clause. This "bracket" structure — with the modal at Position 2 and the infinitive at the end — is a distinctive feature of German that you will encounter again and again.

Both können and müssen have irregular conjugation patterns in the singular forms, but the plural forms follow regular patterns. Learning these two modals opens up a huge range of expression right from the start.

How It Works

Conjugation of können (can, to be able to):

Pronoun	Form
ich	kann
du	kannst
er/sie/es	kann
wir	können
ihr	könnt
sie/Sie	können

Conjugation of müssen (must, to have to):

Pronoun	Form
ich	muss
du	musst
er/sie/es	muss
wir	müssen
ihr	müsst
sie/Sie	müssen

Sentence structure with modals:

Position 2 (Modal)	Middle	End (Infinitive)
Ich kann	gut	schwimmen.
Du musst	morgen	arbeiten.
Können Sie	mir	helfen?

Key points:

• The ich and er/sie/es forms are identical (no ending): ich kann, er kann
• The stem vowel changes in singular: können → kann, müssen → muss
• The infinitive always goes to the end of the clause
• In questions, the modal moves to Position 1: Kannst du schwimmen?
• müssen negated (nicht müssen) means "don't have to" (not "must not" — that would be nicht dürfen)

Examples in Context

German	English	Note
Ich kann schwimmen.	I can swim.	Ability
Du musst arbeiten.	You must work.	Obligation
Können Sie mir helfen?	Can you help me?	Polite request
Er kann gut Deutsch sprechen.	He can speak German well.	Skill
Wir müssen um 8 Uhr da sein.	We have to be there at 8.	Necessity
Ihr könnt hier parken.	You all can park here.	Permission
Sie muss zum Arzt gehen.	She has to go to the doctor.	Obligation
Kannst du mich hören?	Can you hear me?	Question
Ich muss jetzt gehen.	I have to go now.	Immediate necessity
Du musst das nicht machen.	You don't have to do that.	No obligation (not prohibition)

Common Mistakes

Conjugating the main verb instead of leaving it as infinitive

• Wrong: Ich kann schwimme.
• Right: Ich kann schwimmen.
• Why: The main verb must remain in its infinitive form when used with a modal. Only the modal verb is conjugated.

Putting the infinitive in the wrong position

• Wrong: Ich kann schwimmen gut.
• Right: Ich kann gut schwimmen.
• Why: The infinitive goes to the very end of the clause. Other elements (adverbs, objects) sit between the modal and the infinitive.

Confusing "nicht müssen" with "must not"

• Wrong: Thinking Du musst nicht rauchen means "You must not smoke"
• Right: Du musst nicht rauchen = "You don't have to smoke" (no obligation)
• Why: German nicht müssen means "don't have to." For "must not" (prohibition), use nicht dürfen: Du darfst nicht rauchen.

Forgetting that ich and er/sie/es share the same form

• Wrong: Er kannt schwimmen.
• Right: Er kann schwimmen.
• Why: Modal verbs have no ending in the 1st and 3rd person singular: ich kann, er kann (not kannt or kanns).

Practice Tips

1. Daily obligations and abilities: Write five things you can do and five things you must do today: "Ich kann kochen. Ich muss einkaufen gehen."
2. Role-play scenarios: Practice polite requests with können: "Können Sie das bitte wiederholen?" (Can you please repeat that?) This is extremely useful in real life.
3. Bracket visualization: Draw a bracket around each modal sentence, marking Position 2 (modal) and the end (infinitive). This helps internalize the sentence frame.

Related Concepts

• Parent: Regular Verbs (Present) — the regular pattern that modals deviate from
• Modal Verbs: wollen, mögen — expressing wants and likes
• Modal Verbs: dürfen, sollen — permission and suggestions
• Modal Verbs (Subjective Use) — advanced modal meanings