Modal verbs go with an infinitive and indicate how an action is meant. They express permission, ability, preference, necessity, recommendation, or wish, and thereby alter the meaning of the sentence. In a sentence they carry the main grammatical load, while the finite verb infinitive states the actual action. For an overview of auxiliary verbs, 'auxiliary verbs' is useful, and for the form of the second verb the Infinitive.

Dürfen expresses permission and is used when something is allowed. It belongs to the strong modal verbs and combines with an infinitive in the sentence. In the Perfekt and in other compound forms it appears with a double infinitive, which is also common with other modal verbs.

PersonPerson.	FormForm.	BeispielExample.
ichI.	darfmay.	Ich darf gehen, weil die Klasse endet.I may go because the class ends.
duyou.	darfstyou may.	Du darfst hereinkommen, wenn du klopfst.You may come in when you knock.
er, sie, eshe, she, it.	darfmay.	Sie darf bleiben, weil sie eingeladen ist.She may stay because she is invited.
wirwe.	dürfenmay.	Wir dürfen leise sprechen, wenn der Film läuft.We may speak quietly when the movie is running.

Können expresses ability and possibility. It describes what a person can do or what is possible under the given circumstances. As a modal verb it goes with the infinitive of the main verb and forms compound tenses with the infinitive of the main verb and the participle or auxiliary-verb part, not alone, but as part of the modal-verb pattern.

PersonPerson.	FormForm.	BeispielExample.
ichI.	kanncan.	Ich kann schwimmen, wenn das Wasser warm ist.I can swim if the water is warm.
duyou.	kannstyou can.	Du kannst schnell lernen, wenn du übst.You can learn quickly if you practice.
er, sie, eshe, she, it.	kanncan.	Er kann den Fehler finden, wenn er sucht.He can find the error when he searches.
wirwe.	könnencan.	Wir können heute früher gehen, wenn der Plan stimmt.We can leave earlier today if the plan is right.

Mögen expresses a preference and designates what someone likes. In everyday life it is often confused with möchten, which is a polite wish form from Konjunktiv II. Mögen appears with an infinitive only in certain uses, while the most common meaning is a direct preference for things or people.

PersonPerson.	FormForm.	BeispielExample.
ichI.	maglikes.	Ich mag Schokolade, wenn ich müde bin.I like chocolate when I am tired.
duyou.	magstyou like.	Du magst Musik, wenn du arbeitest.You like music when you work.
er, sie, eshe, she, it.	maglikes.	Sie mag den Sommer, wenn die Tage lang sind.She likes the summer when the days are long.
wirwe.	mögento like.	Wir mögen ruhige Abende, wenn wir lesen.We like quiet evenings when we read.

Müssen shows necessity and compulsion. It is used when an action is necessary or cannot be avoided. In combination with the infinitive the main verb remains unchanged, and in the Perfekt the typical compound forms of modal verbs appear.

PersonPerson.	FormForm.	BeispielExample.
ichI.	mussmust.	Ich muss arbeiten, wenn die Frist heute endet.I must work when the deadline ends today.
duyou.	musstyou must.	Du musst gehen, wenn die Tür schließt.You must go when the door closes.
er, sie, eshe, she, it.	mussmust.	Er muss lernen, wenn die Prüfung morgen ist.He must study if the exam is tomorrow.
wirwe.	müssenmust.	Wir müssen bezahlen, wenn wir auschecken.We must pay when we check out.

Sollen expresses recommendation, expectation or instruction. It is often used when another party demands or suggests an action. The verb combines with the infinitive and often appears in command-like statements as an indirect instruction, which is also interesting in connection with the Imperative.

PersonPerson.	FormForm.	BeispielExample.
ichI.	sollshould.	Ich soll früher kommen, wenn der Termin beginnt.I should come earlier when the appointment begins.
duyou.	sollstyou should.	Du sollst das Fenster schließen, wenn es kalt wird.You should close the window when it becomes cold.
er, sie, eshe, she, it.	sollshould.	Sie soll mehr trinken, wenn sie Sport macht.She should drink more when she is playing sports.
wirwe.	sollenshould.	Wir sollen ruhig warten, wenn der Arzt spricht.We should wait quietly when the doctor is speaking.

Wollen expresses desire and intention. It shows what someone intends or actively pursues, and is therefore often close to direct statements about plans. In the Perfekt and in other compound tenses it follows the same periphrastic patterns as the other modal verbs.

PersonPerson.	FormForm.	BeispielExample.
ichI.	willto want.	Ich will kommen, wenn ich Zeit habe.I want to come when I have time.
duyou.	willstyou want.	Du willst helfen, wenn die Arbeit beginnt.You want to help when the work begins.
er, sie, eshe, she, it.	willto want.	Er will reisen, wenn der Sommer kommt.He wants to travel when summer comes.
wirwe.	wollento want.	Wir wollen feiern, wenn alle ankommen.We want to celebrate when everyone arrives.

Weak verbs form the personal forms regularly with the stem and the endings -e, -st, -t and -en. The stem vowel normally stays the same in the present, and the pattern is the basic conjugation form for many common verbs. The infinitive also remains closely tied to this regular pattern with -en or -n.

PersonPerson.	Verbverb.	BeispielExample.
ichI.	spieleI play.	Ich spiele, wenn die Kinder draußen sind.I play when the children are outside.
duyou.	spielstyou play.	Du spielst, wenn du Zeit hast.You play when you have time.
er, sie, eshe, she, it.	spieltplays.	Sie spielt, wenn das Wetter gut ist.She plays when the weather is good.
wirwe.	spielento play.	Wir spielen, wenn alle fertig sind.We play when everyone is finished.

Strong verbs often show a vowel change in the stem and form the simple past (Präteritum) irregularly. They do not follow a uniform ending pattern in the past stem, but must be learned in their forms. A typical example is fahren, which forms fuhr in the simple past, thus clearly showing the strong stem change.

PersonPerson.	Verbverb.	BeispielExample.
ichI.	fuhrdrove.	Ich fuhr, wenn der Zug ausfiel.I drove when the train failed.
duyou.	fährstyou drive.	Du fährst, wenn das Wetter gut ist.You drive when the weather is good.
er, sie, eshe, she, it.	fährtdrives.	Er fährt, wenn er zur Arbeit muss.He drives when he must go to work.
wirwe.	fahrento drive.	Wir fahren, wenn die Familie kommt.We drive when the family comes.

Mixed verbs combine a stem change with a regular simple past ending. They thus appear partly strong and partly weak and form in the simple past usually the ending -te. A common example is bringen, which in the simple past is brachte, thereby clearly showing the mixed form.

PersonPerson.	Verbverb.	BeispielExample.
ichI.	brachtebrought.	Ich brachte das Paket, wenn ich nach Hause ging.I brought the package when I went home.
duyou.	brachtestyou brought.	Du brachtest den Brief, wenn du vorbeikamst.You brought the letter when you passed by.
er, sie, eshe, she, it.	brachtebrought.	Sie brachte Kaffee, wenn Besuch kam.She brought coffee when visitors came.
wirwe.	brachtenbrought.	Wir brachten die Unterlagen, wenn das Büro öffnete.We brought the documents when the office opened.

The infinitive usually ends in -en or -n and denotes the pure verb form without person. The Partizip II is often formed with ge- plus stem plus -t or -en and is important for the Perfekt and other compound tenses. With separable and inseparable prefixes as well as regional variants, the form can vary, but the basic pattern remains recognizable for many verbs.

FormForm.	BildungFormation.	BeispielExample.
InfinitivInfinitive.	Stamm mit enStem with -en.	spielento play.
Partizip IIPast participle.	ge plus Stamm plus tge plus stem plus t.	gespieltplayed.
Partizip IIPast participle.	ge plus Stamm plus enge plus stem plus en.	gefahrendriven.
InfinitivInfinitive.	Stamm mit nStem with -n.	wandernto hike.

In compound tenses modal verbs often appear with a second infinitive, so the infinitive of the main verb appears together with the modal verb. In the Perfekt, this is the typical double infinitive structure with the auxiliary and two infinitives, and in the passive, modal verbs combine with passive constructions to form more complex sentences. These patterns are especially important when modal verbs occur in the past or in formal sentence constructions.

The earliest and most common modal verbs are dürfen, können, müssen, sollen and wollen, because they are used constantly in everyday life. Mögen serves as the verb of preference and is particularly important for firm opinions and expressions of taste. Together they form a core area of the German verb system, which is also fundamental for the Infinitive, Participles, Present Perfect, Subjunctive II, and Imperative.