Proto-Germanic is the reconstructed proto-language of the Germanic branch of the Indo-European languages. It is the hypothetical prehistoric language from which all the Germanic languages, including English, are thought to be descended
Proto-Germanic had only two tenses (past and present), compared to 5-7 in Greek, Latin, Proto-Slavic and Sanskrit. Verbs in Proto-Germanic were divided into two main groups, called "strong" and "weak", according to the way the past tense is formed. Strong verbs use ablaut (i.e. a different vowel in the stem) and/or reduplication (derived primarily from the Proto-Indo-European perfect), while weak verbs use a dental suffix (now generally held to be a reflex of the reduplicated imperfect of PIE *dheH1- originally "put", in Germanic "do"). Strong verbs were divided into seven main classes while weak verbs were divided into five main classes.