Review of the Simple Past Tense

The simple past/imperfect/preterit(e) tense (das Präteritum/das Imperfekt) is the form of the past tense most often found in writing (i.e. narrative form; not to be confused with written dialogue, which maintains the present perfect tense). The spoken past tense in German (the present perfect or “das Perfekt”) typically only utilizes the simple past forms of the following verbs: sein, haben, wollen, sollen, dürfen, müssen, mögen, and können. However, the present perfect form of both ‘sein’ and ‘haben’ are also used in spoken German — for all intents and purposes, they are interchangeable in the spoken word.

Examples:
Present Perfect                                          Simple Past
Ich bin sehr müde gewesen.          OR   Ich war sehr müde.   =   I was very tired.
Ich habe Kopfschmerzen gehabt.  OR   Ich hatte Kopfschmerzen.   =   I had a headache.

Technically speaking, the present perfect sentences could/should be translated with “I have been very tired”, and “I have had a headache”, but this would alter the meaning slightly in English. Based solely on meaning,  the German simple past and present perfect forms are identical in terms of meaning. The only difference between them is that one form (present perfect tense) is exclusively used in spoken German (or other communication construed as verbal such as email, texts, or dialogue), whereas the other (simple past/preterite) is valid for the spoken and written past forms.

The simple past is formed in one of three ways: for regular, mixed, and irregular verbs.

1. The Simple Past of Weak (regular) Verbs. 

Regular verbs are verbs that show no stem changes in any tense or for any pronoun. 
For example, the stem of the verb “kochen” (to cock) is “koch-“, and it remains “koch-” in every sense and pronoun. 

Example: 
Ich koche – I cock. Ich kochte – I cooked. Ich habe gekocht. – I have cooked. 

The past participle of regular verbs is formed with “ge” and ends on -t (gekocht) 

Example:
Ich spiele Fussball. Ich spielte Fussball. Ich habe Fussball gespielt. 
I play soccer. I played soccer. I have played soccer. 

2. Strong (Irregular) Verbs

The term “irregular” verb applies to two groups. “Strong” and “mixed” verbs. Technically speaking, any verb that shows a stem change (vowel change, vowel addition, etc) is an irregular verb. Strong verbs are irregular verbs that have a stem change in one of the tenses or pronouns, and their past participle ends on “-en”. 
Note: a stem change might only appear in the simple past). 

Although there are no set rules for predicting the past tense forms of irregular verbs, a number of verbs in English exhibit similar patterns of vowel changes as those in German (e.g. sing – sang – sung / singen – sang – gesungen). In German there are seven approximate categories of vowel change patterns, from infinitive to simple past to past participle (e.g. ride-rode-ridden):

1. ei – ie – ie / ei – i – i = bleiben – blieb – geblieben / reiten – ritt – geritten
2. ie – o – o / e – o – o = verlieren – verlor – verloren / heben – hob – gehoben
3. i – a – u / i – a – o = singen – sang – gesungen / beginnen – begann – begonnen
4. e – a – o = nehmen – nahm – genommen
5. e – a – e / i – a – e / ie – a – e = essen – ass – gegessen / bitten – bat – gebeten / liegen – lag – gelegen
6. a – u – a = einladen – lud ein – eingeladen
7. a – ie – a / au – ie – au / ei – ie – ei / u – ie – u / o – ie – o / a – i – a = gefallen – gefiel – gefallen / laufen – lief – gelaufen / heißen – hieß – geheißen / rufen – rief – gerufen / stoßen – stieß – gestoßen / fangen – fing – gefangen

Example: 
Ich fahre in die Arbeit. Ich fuhr in die Arbeit. Ich bin in die Arbeit gefahren. 
I drive to work. I drove to work. I have driven to work. 

3. Mixed Verbs

Mixed verbs are also irregular, but they get their name from the fact that, while they do have a stem change somewhere in their conjugation (either in tense or in pronoun), which is what they have in common with strong verbs, their participle ends on “-t” which they have in common with weak verbs. 

Examples:
Ich bringe einen Kuchen. Ich brachte einen Kuchen. Ich habe einen Kuchen gebracht. I bring a cake. I brought a cake. I have brought a cake. 

4. Modal Verbs

Modal verbs are commonly used in their preterite/simple past form in both written and spoken German, and their meanings are identical. Although the present perfect forms do exist, they are only used when they are not accompanied by another verb. Notice that the umlauts are dropped when forming the past tense of these verbs.
(Do you really have to leave? Yes, I have to (leave.)

You will note that the 1st- and 3rd-person singular forms of these verbs are identical, and a “t” is added to the end of the stem before applying the ending. In keeping with the phonological rule related to stems ending in a “d” or “t”, an “e” must be added before applying the conjugated verb endings (ihr and du forms). Thus, the du form of sollen would add a “t” + “e” + “st” for its simple past form, solltest. Of course, this makes no real difference when adding the ‘en’ ending to the wir, sie, and Sie plural forms, as no additional “e” separating the “t” from the ending is necessary. Note also that the ich, er, sie, and es forms add the “t” and then “e” only. Effectively, the simple past ending that is added to the modals and regular verbs is simply a “t” at the end of the stem.

N.B. The simple past forms of the modal verbs are the basis for the formation of the general subjunctive (modals with an umlaut in their infinitive forms)