Präteritum

The Präteritum is formed as follows.

When the verb stem ends in -d, -t, an "e" is added to the ending in the 2nd and 3rd person singular and in the 2nd person plural.

The same rule applies to verbs with a stem that ends in a consonant + -m, -n *

* Exception: When an -r comes before -m or -n , e.g. in verbs like formen, wärmen, lernen, turnen.