German verbs always end in –n in their infinitive form, usually –en:

When introducing verbs, most textbooks and classes jump right into conjugation (I work, you work, he works…) but let’s take a few minutes first to understand the big picture. German root verbs can be broken into five categories:

All five of these categories have close parallels in English. Here’s what they mean:

• Auxiliary (“helping”) verbs are used with other verbs to form compound tenses, like the future tense in English (I will find it) and German (Ich werde es finden)
• Modal verbs are used with other verbs to indicate their modality, which means the desire, ability, permission or obligation to do them: “You must listen to me!” (“Du musst mir zuhören!”)
• Strong verbs form the past (preterite) tense with a vowel shift, like "swim / swam" in English (schwimmen / schwammen in German). Strong verbs in German have an irregular participle form that ends in –n, which is also true of many strong verbs in English (I choose, I chose, I have chosen). But more on all that later.
• Weak verbs form the past tense with a hard consonant added at the end, t in German and d (or sometimes t) in English. Learn is a weak verb in both English (I learn, I learned [US] or learnt [UK]) and German (ich lerne, ich lernte)
• Mixed verbs get their name because they form the past tense with both a vowel shift and a hard consonant sound at the end. Bring is a mixed verb in both English (we bring/we brought) and German (wir bringen/wir brachten)

If you’re familiar with the concept of regular and irregular verbs in English or another language, you can think of the weak / strong distinction in German as more or less the same thing. Weak verbs in German are all regular, which means that once you know the infinitive you can form any other conjugation in standard ways. For the other four types, you have to memorize a few other forms when you learn the verb.

We said above that there are thousands of weak verbs, which is technically true, but don't let it scare you: there are at most a few hundred that you really need to know. After that, the vast majority of German verbs in common usage are:

• formed by adding prefixes to the root verbs above -- we'll cover this in Section V.11;
• obvious derivations of a non-verb -- for example, if you know that mehr means "more," it'll be clear in context that mehren is "to increase."
• obvious Germanizations of foreign verbs, including the -ieren verbs (covered in V.4) and many modern tech-related terms like "adden" (on a social network)

In both German and English, there’s a tendency for strong and mixed verbs to become weak over time, i.e. for people to start treating them as regular verbs. At any given point, there are certain verbs that are still completely strong (you can’t say "I falled" rather than "I fell"), certain verbs where the strong form is almost gone (to say "children clad in rags" rather than "clothed in rags" would sound a little pretentious in modern English), and some where it's been gone so long that few people today have even heard it, though it often still counts in Scrabble (like "holp" for "helped"). A few are somewhere in between: for example, "dived" and "dove" both sound OK to most people today, but in a few decades "dived" may have completely taken over.

In any event, some sources don't do enough to distinguish the strong forms that are mandatory from those that sound old-fashioned or silly. In our list of strong verbs we try to make the distinctions a little more clear.