What are the rules to build the past tense in German?

Answer 1

As in English, the simple past tense (preterite) in German (Präteritum) is used to describe an action or event within a time frame that is completed, e.g.

Gestern rannte ich nach Hause - I ran home yesterday.

However it is normal for native German speakers to use the present perfect (Perfekt) in lieu of the simple past tense, e.g.

Gestern bin ich nach Hause gerannt - lit. I have run home yesterday but in the sense of I ran home yesterday.

When forming the simple past, weak verbs add -(e)te, -(e)test, -(e)ten, or -(e)tet to the stem:

Ich sagte das. I said that.

Wir machten die Tür zu. We closed the door

Du kauftest zu viel. You bought too much.

Ihr wohntet neben uns. You all lived next to us

Sie arbeiteten hart. You worked hard.

Es regnete stark. It rained hard.

Sie redeten viel. They talked a lot.

Irregular weak verbs and auxiliary modals add the same endings as above to a (usually) changed stem:

Ich wollte das hören. I wanted to hear it.

Wir durften das nicht sagen We weren't allowed to say that.

Du konntest das nicht wissen You couldn't know that.

Sie nannten ihn Hans They named him Hans.

Strong verbs (usually) change the stem and add either no ending or -st, -en, or -t:

Ich ging nach Hause. I went home.

Sie las das Buch. She read the book.

Du sprachst zu schnell. You spoke too quickly.

Sie schrieben es auf Deutsch. They wrote it in German.

Ihr halft uns nicht. You didn't help us.

When using verbs with separable prefixes the prefix goes to the end of the sentence:

Sie brachte ihren neuen Freund mit. She brought her new boyfriend along.

Er rief seine Mutter nie an. He never rang his mother.

In spoken German, the simple past tense is often perceived as too formal, so colloquial passages often use the present perfect:

Ich bin nach Hause gegangen und habe die Koffer gepackt - lit. I have gone home and packed the suitcases but in the sense of I went home and packed the suitcases.

The use of present perfect instead of simple past is not considered incorrect by German speakers but is based on the fact that many German dialects simply don't have a simple past (preterite) tense.