Conjugation classes, e.g. strong verbs with change of vowel versus weak verbs with a t-suffix to express tense represent formal differentiations without functional equivalent. Thus, at first glance, they appear to complicate the language system. This study shows that conjugation classes by no means must be necessarily downgraded in the history of Germanic languages but rather maintained and reorganized. On the other hand it shows that their change is not arbitrary but steered by principles, e.g. linked functionally to grammatical categories such as tense.