The modal verbs express a way or “mode” of doing things that complements the main verb (i.e. the verb that carries the most meaning) in the sentence. In the example below, the modal verb “wollen” (to want) changes the meaning of the sentence and is conjugated and placed in second position. The main verb “spielen” (to play) is moved to the end of the sentence in its infinitive form.
Der Junge spielt gern Fußball. The boy likes to play soccer.
Der Junge will Fußball spielen. The boy wants to play soccer.
Note that, in the first sentence, the adverb “gern” is added to indicate a like for an activity (soccer); however, the adverb comes directly after the main verb and does not change the placement of the verb “spielen.” By contrast, the second sentence includes the modal verb “wollen” conjugated (“will”) in the second position, which “kicks” the main verb (“spielen”) to the end of the sentence.
Modal verbs in German are conjugated differently than other verbs in the present tense — most notably in the case of the first- and third-person singular forms. Each of these two forms drops an ending (‘e’ and ‘t’, respectively) and are identical. Note that, unlike in the present tense of most verbs, the first-person or ‘ich’ form of modal verbs exhibits a stem-vowel change.
The modal verbs have similar meanings to their English counterparts:
wollen – to want to
können – can, to be able to
müssen – must, to have to
sollen – shall, to be supposed to
dürfen – may, to be permitted/allowed to
mögen – may, to like
The modal verb “sollen” is not translated here as “should,” even though in English it is often used interchangeably with indicative and subjunctive (e.g. I am supposed to clean the kitchen (indicative = obligation) VS. I should clean the kitchen before it becomes a total mess (subjunctive = hypothetical)). Native speakers often use “should” in place of “supposed to,” but in German there is a difference between using “sollen” (indicative) and “sollten” (subjunctive).
Another nuanced meaning to be clarified is “mögen.” This modal verb appears to be readily substituted for “dürfen” because of the definition “may”; however, this is not the case. When using the modal verb “mögen” to mean “may,” it is typically part of an idiom (e.g. es mag sein / it may be; wie immer es sein mag / as the case may be). The English modal “might” is typically constructed in German using a form of “können,” not unlike another English equivalent: “it might be” is essentially the same as “it could be.”