German verbs : weak, strong and irregular
Verbs in German, as in English, may be weak, strong or irregular.
1) Weak verbs are verbs which retain the SAME stem vowel throughout;
2) strong verbs are those which systematically CHANGE the stem vowel;
3) and irregular verbs ( which could be said to have a mixed conjugation, to use the term employed for a similar phenomenon in noun and adjective declension) have some characteristics of each of the other two groups.