Regular Verbs:
Regular verbs follow predictable patterns in their conjugation. There are several categories of regular verbs based on their stem vowel changes and the endings used:
* -en verbs (most common): These verbs add the endings *-te*, *-test*, *-te*, *-ten*, *-tet*, *-ten* to their stem in the Präteritum. The past participle is formed with *ge-* + stem + *-t*. Examples:
* lieben (to love): ich liebte, du liebtest, er liebte, wir liebten, ihr liebtet, sie liebten; Partizip II: geliebt
* arbeiten (to work): ich arbeitete, du arbeitetest, er arbeitete, etc.; Partizip II: gearbeitet
* -eln, -ern verbs: These verbs often have slight stem changes in the Präteritum. They follow a similar pattern with added endings. Examples:
* spielen (to play): ich spielte, du spieltest, er spielte, etc.; Partizip II: gespielt
* lernen (to learn): ich lernte, du lerntest, er lernte, etc.; Partizip II: gelernt
Irregular Verbs:
Irregular verbs do *not* follow predictable patterns. Their past tense and past participle forms are often drastically different from their infinitive form, and there's no consistent rule to predict them. They must be memorized individually. Examples:
* sein (to be): Präteritum: war, warst, war, waren, wart, waren; Partizip II: gewesen
* haben (to have): Präteritum: hatte, hattest, hatte, hatten, hattet, hatten; Partizip II: gehabt
* gehen (to go): Präteritum: ging, gingst, ging, gingen, gingt, gingen; Partizip II: gegangen
* sehen (to see): Präteritum: sah, sahst, sah, sahen, saht, sahen; Partizip II: gesehen
In short: If you can predict the past tense and past participle forms based on a consistent pattern (adding *-te*, *-t* etc. to the stem), it's a regular verb. If the forms are unpredictable and must be memorized, it's an irregular verb.
A significant number of verbs in German are irregular, making memorization a crucial part of learning the language. Using verb conjugation tables is highly recommended.