In the Germanic languages, a strong verb is a verb that marks its past tense by means of changes to the stem vowel (ablaut). The majority of the remaining verbs form the past tense by means of a dental suffix (e.g. -ed in English), and are known as weak verbs. In modern English, strong verbs include sing (present I sing, past I sang, past participle I have sung) and drive (present I drive, past I drove, past participle I have driven), as opposed to weak verbs such as open (present I open, past I opened, past participle I have opened). Not all verbs with a change in the stem vowel are strong verbs, however; they may also be irregular weak verbs such as bring, brought, brought or keep, kept, kept. The key distinction is that most strong verbs have their origin in the earliest sound system of Proto-Indo-European, whereas weak verbs use a dental ending (in English usually -ed or -t) that developed later with the branching off of Proto-Germanic. In modern English, as in all modern Germanic languages, weak verbs outnumber strong verbs. The "strong" vs. "weak" terminology was coined by the German philologist Jacob Grimm in the 1800s, and the terms "strong verb" and "weak verb" are direct translations of the original German terms and . Origin and development Strong verbs have their origin in the ancestral Proto-Indo-European (PIE) language. In PIE, vowel alternations called ablaut were frequent and occurred in many types of word, not only in verbs. The vowel that appeared in any given syllable is called its "grade". In many words, the basic vowel was *e (e-grade), but, depending on what syllable of a word the stress fell on in PIE, this could change to *o (o-grade), or disappear altogether (zero grade). Both e and o could also be lengthened to ē and ō (lengthened grade). Thus ablaut turned short e into the following sounds: As the Germanic languages developed from PIE, they dramatically altered the Indo-European verbal system. PIE verbs could occur in three distinct aspects: the aorist, present and perfect aspect. The aorist originally denoted events without any attention to the specifics or ongoing nature of the event ("ate", perfective aspect). The present implied some attention to such details and was thus used for ongoing actions ("is eating", imperfective aspect). The perfect was a stative verb, and referred not to the event itself,