What are modal verbs?
Modal verbs almost always appear together with another verb. They change the meaning of that action: Is it possible? Necessary? Permitted? Wanted?
mögen is a special case: as a modal verb it expresses a liking, but without an infinitive. möchten is actually the Konjunktiv II of mögen, but it is used like its own modal verb. You almost never use the past tense of möchten; you use wollte instead.
Meaning of the modal verbs
können: ability or possibility
müssen: no alternative
dürfen: permission or prohibition
wollen: own wish
sollen: task from someone else
möchten: polite wish
mögen: to like something
Present tense conjugation
Unlike most verbs in the present tense, modal verbs have irregular forms. Important: ich and er/sie/es are always the same. Both without -t. For the past, you usually use the simple past (ich konnte, ich musste).
Word order: modal verb + infinitive
The modal verb stands conjugated in position 2. The main verb stands as an infinitive at the end of the sentence. A nicht goes directly before the infinitive (Ich muss heute nicht arbeiten).
Exercises
Three short tasks: distinguish können/müssen, dürfen/sollen, wollen/mögen.
können or müssen?
Choose the appropriate modal verb.
dürfen or sollen?
Choose the correct modal verb.
wollen or mögen?
Decide which modal verb fits.
Modal verbs in the past
Fill in the modal verb in the Präteritum. Remember: the Präteritum drops the umlaut (konnte, musste, durfte).