no umlaut of , but , with umlaut of . Present stem Umlaut in weak verbs () The German word ("reverse umlaut"), sometimes known in English as "unmutation", is a term given to the vowel distinction between present and preterite forms of certain Germanic weak verbs. These verbs exhibit the dental suffix used to form the preterite of weak verbs, and also exhibit what appears to be the vowel gradation characteristic of strong verbs. Examples in English are think/thought, bring/brought, tell/told, sell/sold. The phenomenon can also be observed in some German verbs including ("burn/burnt"), ("know/knew"), and a handful of others. In some dialects, particularly of western Germany, the phenomenon is preserved in many more forms (for example Luxembourgish , "to put", and Limburgish , "to tell, count"). The cause lies with the insertion of the semivowel between the verb stem and inflectional ending. This triggers umlaut, as explained above. In short stem verbs, the is present in both the present and preterite. In long stem verbs however, the fell out of the preterite. Thus, while short stem verbs exhibit umlaut in all tenses, long stem verbs only do so in the present. When the German philologist Jacob Grimm first attempted to explain the phenomenon, he assumed that the lack of umlaut in the preterite resulted from the reversal of umlaut. In actuality, umlaut never occurred in the first place. Nevertheless, the term "Rückumlaut" makes some sense since the verb exhibits a shift from an umlauted vowel in the basic form (the infinitive) to a plain vowel in the respective inflections. Umlaut as a subjunctive marker In German, some verbs which display a back vowel in the past tense undergo umlaut in the subjunctive mood: (ind.) → (subj.) ("sing/sang"); (ind.) → (subj.) ("fence/fenced"). Again, this is due to the presence of a following in the verb endings in the Old High German period. Historical survey by language West Germanic languages Although umlaut operated the same way in all the West Germanic languages, the exact words in which it took place and the outcomes of the process differ between the languages. Of particular note is the loss of word-final after heavy syllables. In the more southern languages (Old High German, Old Dutch, Old Saxon), forms that lost often show no umlaut, but in the more northern languages (Old English, Old Frisian), the forms do. Compare Old English "guest", which shows umlaut, and