The simple past or imperfect tense in German is used primarily in written form; however, certain verbs are often used in the simple past in spoken German. These verbs include: sein, haben, dürfen, können, mögen, sollen, wollen, and müssen. These auxiliary verbs (helping and modal verbs) have the following forms in the imperfect:
Hilfsverben (Helping Verbs)
Modalverben (Modal Verbs)
These verbs in the imperfect are identical in meaning to their forms in the present perfect tense (e.g. ist gewesen = war ). You will note that the 1st- and 3rd-person singular forms of these verbs are identical, all umlauts disappear, and, at least for haben and the modal verbs, 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 (see below) is simply a “t” at the end of the stem.
Regelmäßige Verben (Regular Verbs)
As seen in the above chart of regular verbs in the simple past, the only new change from the modal verbs is that any regular verbs whose stems end in “d” or “t” must add an “e” before the “t” simple past ending, which is why arbeiten becomes arbeitetest in the du form — the first “t” must be followed by an “e” in order to pronounce the second “t.” Other verbs that also add an “e” before the “t” are those that do so in the present tense, including atmen, begegnen, leugnen, widmen, and zeichnen (e.g. Er zeichnete/widmete/begegnete).
Unregelmäßige Verben (Irregular Verbs)
Irregular verbs, such as geben, sprechen, and ziehen, have stem vowel changes in the imperfect tense (e.g. sie gab/sprach/zog), and they have no endings for 1st- and 3rd-person singular forms (still identical). All other endings are normal (e.g. + “st” for du form, + “en” for wir, Sie, sie plural forms). Remember, whenever a stem ends in “d” or “t” — like finden (fanden in simple past) — an “e” is inserted between the the “d” or “t” stem ending and conjugated endings “st” and “t.”
Gemischte Verben (Mixed Verbs)
Mixed verbs have elements of both regular and irregular verbs in the simple past tense: they exhibit stem (vowel) changes and have the “t” ending added to the stem. The above verbs are some of the most common mixed verbs, though there are several more in German.
The simple past/imperfect/preterite tense is the basis for the general subjunctive (der Konjunktiv II), which is explained in greater detail here.