German Modal Verbs *können* and *müssen*

In Brief

Use können for ability or possibility (“can”) and müssen for necessity (“must,” “have to”). Conjugate the modal verb and put the other verb in the infinitive (its basic dictionary form) at the end: Ich kann schwimmen and Du musst arbeiten. Be careful with negatives: Du musst nicht kommen normally means “You do not have to come,” not “You must not come.”

Overview

The verbs können and müssen are modal verbs: they combine with another verb and add an idea such as ability, possibility, or necessity. They let you say that someone can do something, has to do something, or cannot do something. These are essential A1 verbs because they appear constantly in plans, requests, rules, work, travel, and everyday conversation.

German and English use similar ideas, but their sentence structures differ. English keeps “can” or “must” beside the following verb: “I can swim.” In a basic German statement, the conjugated modal occupies the normal verb position, while schwimmen moves to the end: Ich kann schwimmen. This two-part structure is often called a sentence bracket because the two verbs frame the middle of the clause.

The beginner rule is dependable: choose the right present-tense modal form, keep the second verb as an infinitive, and send that infinitive to the end. Later sections explain subordinate clauses, omitted infinitives, past forms, and meanings that go beyond simple ability and obligation.

How It Works

What the two verbs mean

Können most often expresses:

• ability or learned skill: Mia kann gut kochen. — Mia can cook well.
• practical possibility: Wir können morgen fahren. — We can go tomorrow.
• a polite request, especially as a question: Können Sie mir helfen? — Can you help me?
• general possibility: Im April kann es noch schneien. — It can still snow in April.

Müssen most often expresses:

• necessity or obligation: Ich muss heute arbeiten. — I have to work today.
• a requirement caused by circumstances: Wir müssen den Bus nehmen. — We have to take the bus.
• a strong conclusion at more advanced levels: Er muss krank sein. — He must be ill.

English “must” can sound formal or forceful, while German müssen is the ordinary way to express “have to” as well as “must.” Therefore, Ich muss los can naturally mean “I have to go.”

Present-tense conjugation

Both verbs are irregular. In the singular, their stem vowel changes, and the first- and third-person singular forms have no ending. The plural forms resemble the infinitive.

Person	können	müssen	English guide
ich	kann	muss	I can / must, have to
du	kannst	musst	you can / must, have to
er / sie / es	kann	muss	he / she / it can / must, has to
wir	können	müssen	we can / must, have to
ihr	könnt	müsst	you all can / must, have to
sie / Sie	können	müssen	they / you (formal) can / must, have to

Notice where the umlaut appears. The singular forms are kann, kannst, kann and muss, musst, muss, without an umlaut. The plural forms retain ö or ü: können, könnt and müssen, müsst. Writing ich könne or ich müsse for an ordinary present-tense statement is incorrect; those forms belong to the subjunctive, a later topic.

Statements: conjugated modal second, infinitive last

In a main-clause statement, the finite verb (the verb form that changes for person and tense) normally occupies position two. With a modal construction, that finite verb is können or müssen. The infinitive goes to the end.

Subject + conjugated modal + middle information + infinitive

• Ich kann heute länger bleiben. — I can stay longer today.
• Wir müssen um acht Uhr anfangen. — We have to start at eight.

“Position two” means the second sentence unit, not necessarily the second word. If another element comes first, the subject follows the modal:

• Heute kann ich länger bleiben. — Today I can stay longer.
• Um acht Uhr müssen wir anfangen. — At eight we have to start.

The infinitive does not receive a personal ending. Say Du musst arbeiten, not Du musst arbeitest.

Questions

In a yes/no question, the conjugated modal comes first. The infinitive remains at the end:

• Kannst du morgen kommen? — Can you come tomorrow?
• Müssen wir hier warten? — Do we have to wait here?

In a question with a question word, the question word comes first and the modal follows:

• Wann kannst du kommen? — When can you come?
• Warum müsst ihr so früh gehen? — Why do you have to leave so early?

Formal Sie takes the same form as plural sie: Können Sie mir helfen? Capitalization identifies formal “you” in writing.

Negation and the important meaning of nicht müssen

Place nicht according to what is being negated, but remember this crucial contrast:

German	Natural English meaning
Ich kann nicht kommen.	I cannot come.
Du musst nicht kommen.	You do not have to come.
Du darfst nicht kommen.	You must not come. / You are not allowed to come.

With können, negation usually removes ability or possibility. With müssen, negation removes the necessity: the action is optional. English speakers often read nicht müssen as “must not,” but prohibition in German is normally expressed with nicht dürfen.

Compare:

• Du musst die Rechnung nicht heute bezahlen. — You do not have to pay the bill today.
• Du darfst hier nicht bezahlen. — You must not pay here / Payment is not allowed here.

The exact position of nicht can shift the emphasis. At A1, the safest pattern is to put it before the final infinitive when negating the action as a whole: Ich kann heute nicht kommen.

Separable verbs stay together in the infinitive

A separable verb has a prefix that can split off in an ordinary main clause, such as aufstehen (“get up”). After a modal, it remains an unsplit infinitive at the end:

• Without a modal: Ich stehe um sechs Uhr auf.
• With a modal: Ich muss um sechs Uhr aufstehen.

Do not say Ich muss um sechs Uhr stehen auf.

Examples in Context

German	English	Note
Ich kann schwimmen.	I can swim.	Ability; kann agrees with ich.
Du musst arbeiten.	You must work. / You have to work.	Everyday necessity.
Können Sie mir helfen?	Can you help me?	Polite request with formal Sie.
Meine Schwester kann sehr gut kochen.	My sister can cook very well.	Learned skill.
Wir können am Samstag ins Museum gehen.	We can go to the museum on Saturday.	Practical possibility or suggestion.
Kannst du das Fenster öffnen?	Can you open the window?	Informal request.
Im Winter kann es hier sehr kalt werden.	It can get very cold here in winter.	General possibility.
Heute muss ich länger im Büro bleiben.	Today I have to stay longer at the office.	The time phrase comes first; the modal remains second.
Ihr müsst eure Tickets mitbringen.	You all have to bring your tickets.	Plural informal ihr.
Müssen wir jetzt bezahlen?	Do we have to pay now?	Yes/no question.
Warum musst du so früh aufstehen?	Why do you have to get up so early?	aufstehen stays together after a modal.
Ich kann heute leider nicht kommen.	Unfortunately, I cannot come today.	Negated ability or possibility.
Sie müssen morgen nicht arbeiten.	You do not have to work tomorrow.	No necessity; working is optional.
Der Schlüssel muss in der Küche sein.	The key must be in the kitchen.	Advanced: a strong conclusion, not an obligation.

Common Mistakes

Conjugating both verbs

• Wrong: Du musst arbeitest.
• Right: Du musst arbeiten.
• Why: Only the modal is conjugated. The other verb stays in the infinitive at the end.

Leaving the infinitive beside the modal

• Wrong: Ich kann schwimmen sehr gut.
• Right: Ich kann sehr gut schwimmen.
• Why: In a basic German main clause, the infinitive closes the sentence bracket.

Using the infinitive instead of the singular form

• Wrong: Ich können Deutsch sprechen.
• Right: Ich kann Deutsch sprechen.
• Why: Ich requires kann. The infinitive können is also the present form for wir, sie, and formal Sie, but not for ich.

Adding an umlaut to singular present forms

• Wrong: Er müsst heute lernen.
• Right: Er muss heute lernen.
• Why: The singular forms of müssen lose the umlaut. Müsst belongs to ihr.

Translating “must not” as nicht müssen

• Wrong for a prohibition: Du musst hier nicht rauchen.
• Right: Du darfst hier nicht rauchen.
• Why: Du musst nicht rauchen means “You do not have to smoke.” Use nicht dürfen when something is forbidden.

Splitting a separable infinitive

• Wrong: Wir müssen morgen kaufen ein.
• Right: Wir müssen morgen einkaufen.
• Why: A separable verb splits in some ordinary main clauses, but it remains whole when it is the infinitive after a modal.

Usage Notes

Requests with können

Können Sie ...? and Kannst du ...? are common ways to make requests. As in English, a request may technically ask about ability while pragmatically asking someone to act:

• Können Sie das bitte wiederholen? — Could you repeat that, please?
• Kannst du kurz warten? — Can you wait a moment?

Adding bitte makes the request more explicitly polite. German also uses the subjunctive form könnten for softer requests—roughly “could”—but you do not need it to apply the basic A1 pattern.

Müssen is not automatically harsh

Because English “must” may sound official, learners sometimes avoid müssen. In German, it is a neutral, frequent verb for ordinary necessity: Ich muss einkaufen is simply “I have to go shopping.” Tone and context determine whether it sounds like an order.

The infinitive can be understood and omitted

German sometimes uses a modal without stating another verb when the missing action is obvious:

• Ich kann Deutsch. — I can speak/use German.
• Ich muss nach Hause. — I have to go home.
• Kannst du morgen? — Are you available / Can you make it tomorrow?

These are normal expressions, not broken sentences. As a beginner, use the full pattern when the intended action would not be clear.

Beyond the Basics: Later Uses and Structures

You do not need to master this section at A1, but these patterns explain forms you will soon encounter.

Subordinate clauses

A subordinate clause is a clause introduced by a word such as weil (“because”) that depends on another clause. Its conjugated verb normally moves to the end. With a modal, the infinitive comes immediately before the conjugated modal:

• Ich gehe früh ins Bett, weil ich morgen arbeiten muss. — I am going to bed early because I have to work tomorrow.
• Sie kommt mit, wenn sie früher gehen kann. — She is coming along if she can leave earlier.

Compare the main clause Ich muss morgen arbeiten with weil ich morgen arbeiten muss.

Past time

The simple past forms konnte and musste are very common, including in speech:

Person	können (simple past)	müssen (simple past)
ich / er / sie / es	konnte	musste
du	konntest	musstest
wir / sie / Sie	konnten	mussten
ihr	konntet	musstet

• Gestern konnte ich nicht kommen. — I could not come yesterday.
• Wir mussten lange warten. — We had to wait a long time.

The perfect tense is more complex. With another verb, German normally uses a double infinitive: Ich habe lange arbeiten müssen (“I had to work for a long time”), not the regular participle gemusst. This pattern is worth recognizing, but the simple past musste and konnte is often easier and more natural.

Ability, possibility, and deduction

Können does not always refer to a skill. It can mark something as possible: Das kann passieren (“That can happen”). Negated können can reject a possibility: Das kann nicht stimmen (“That cannot be right”).

Müssen can express a logical conclusion rather than a duty:

• Das Licht ist an. Jana muss zu Hause sein. — The light is on. Jana must be at home.

Context tells you whether müssen means obligation or deduction. A person in Jana muss arbeiten may be obliged to work; in Jana muss krank sein, the speaker is drawing a conclusion.

Kennen is not können

English “know” and “can” overlap in phrases about knowing how to do something, but German keeps the verbs distinct. Können expresses ability: Ich kann Ski fahren (“I can ski”). Kennen means being acquainted with a person, place, or thing: Ich kenne Berlin (“I know Berlin”). Do not use kennen for a skill.

Practice Tips

1. Build sentence brackets aloud. Choose a subject and modal first—Ich kann ..., Wir müssen ...—then add details and finish with an infinitive. Pause slightly before the final verb until the word order becomes automatic.
2. Drill the singular and plural contrast. Say pairs such as ich kann / wir können, du musst / ihr müsst, and er muss / sie müssen. This trains both the ending and the umlaut change.
3. Practice the negative contrast with real rules. Make pairs such as Ich muss heute nicht arbeiten (no necessity) and Ich darf hier nicht parken (prohibition). Always ask: “Is this optional, or is it forbidden?”

Related Concepts

• Prerequisite: Regular Verbs in the Present — provides the basic ideas of verb conjugation and infinitives.
• Next step: Modal Verbs wollen and mögen — adds wishes, intentions, preferences, and polite möchten.
• Next step: Modal Verbs dürfen and sollen — covers permission, prohibition, advice, and reported expectations.
• Advanced: Subjective Uses of Modal Verbs — develops meanings of probability, inference, and reported information.