Formation in different tenses


Modal verbs are quite irregular in German. Here is a summary of their forms in different tenses.

Present tense

In the present tense only sollen doesn’t change its stem vowel in the ich, du and er/sie/es forms. Note also that the first and third person singular (ich and er/sie/es) have identical forms and don’t have their usual present tense endings.

ichdarfkannmagmusssoll will
du darfstkannstmagstmusstsollstwillst
ihr dürftkönntmögtmüsstsolltwollt
Sie dürfenkönnenmögenmüssensollenwollen
sie dürfenkönnenmögenmüssensollenwollen

Present perfect tense

The past participle of the six modals are: gedurft, gekonnt, gemocht, gemusst, gesollt, gewollt. However, these forms are rarely used and are usually replaced with the simple past forms of the modals:
present perfect→Sie hat den Film nicht gemocht. 
simple past→ Sie mochte den Film nicht.
She didn’t like the film.

When the modal appears together with another verb, the present perfect tense is constructed with haben + infinitive of the second verb + infinitive of the modal:

Hugo hat noch bis spät arbeiten müssen.
Hugo (has) had to work late.
Eva hat noch einen Kaffee trinken wollen.
Eva wanted to drink another coffee.

Note that as the infinitive of the modal verb is used instead of the past participle form, the sentence finishes in two infinitives (double infinitive construction). This present perfect structure is often avoided by using the simple past tense: Hugo musste noch bis spät arbeiten → Eva wollte noch einen Kaffee trinken.

Simple past tense

Modal verbs form their simple past tense by dropping the umlaut and by using -te endings:

ichdurftekonntemochtemusstesollte wollte
er/sie/es durftekonntemochtemusstesolltewollte

Sie durfte nicht ins Kino gehen.
he was not allowed to go to the cinema.
Er konnte sehr gut tanzen.
He could dance very well.
Wolltest du etwas fragen?
Did you want to ask something?
Wir mochten die Musik nicht.
We didn’t like the music.

Past perfect tense

If the modal verb stands on its own, the past perfect tense is constructed with the past tense of haben + the past participle of the modal. When the modal verb appears together with another verb, the past perfect tense is constructed with the infinitive of the second verb + the infinitive form of the modal:

Er hatte das nicht gewollt.
He had not wanted this.
Ich hatte Tom Hanks interviewen dürfen.
I had been allowed to interview Tom Hanks.

Future tense

The future tense of modal verbs is constructed with the finite form of werden + the  of the main verb + the infinitive of the modal:

Pavarotti wird nicht singen können.
Pavarotti won’t be able to sing.
Sie wird ein neues Auto kaufen müssen.
She will have to buy a new car.