For some verbs, such as essen, the conjugations for du and er, sie, es are irregular. Instead of following the pattern and becoming esst, the vowel is changed to i, making it isst. Another example is fahren which becomes fährst and fährt respectively.

What is the origin of this peculiar behavior and is there an easier way to know which verbs change other than just remembering them?

  • 2
    I'm afraid you're stuck with memorizing - there is no clear rule that I'm aware of, and these things tend to change over time
    – Hulk
    Commented Nov 13, 2014 at 6:22
  • 1
    Each word has its own history. You can hardly answer this question. Here are some links (in German) that might help you: starke-verben-ablautreihen-konjugation, Wie beugt man starke Verben?, Warum gibt es im Deutsch starke und schwache Verben?
    – Em1
    Commented Nov 13, 2014 at 9:39
  • @Em1: You are right: Each word has its own history. However, sometimes/often there are patterns that can help you understand why things are as they are and memorize them. (In my opinion, the worst thing that you can do to students/learners is to say: everything irregular, you have to learn it by heart.)
    – Chris
    Commented Nov 13, 2014 at 14:39
  • Yes, an old teacher of mine in the Irish language pointed out that it is in fact the most common verbs that will have the most variation and irregularity.
    – cheznead
    Commented Jul 14, 2015 at 22:26

3 Answers 3


There are two main classes in German verb conjugation: Strong verbs are verbs that form their past tense with ablaut (singen - sang - gesungen); weak verbs are verbs that form their past tense with a dental suffix (leben - lebte - gelebt).

The phenomenon that you describe (vowel change in present singular) is primarily one that occurs in strong verb conjugation. It can be explained by looking at the verb endings of Old High German strong verbs in present tense:

infinitive: werfan
1st person singular: ih wirfu
2nd person singular: dû wirfis
3rd person singular: er wirfit
1st person plural: wir werfemês/werfên
2nd person plural: ir werfet
3rd person plural: sie werfent

As you can see, the OHG present tense endings in singular for strong verbs are -u/-is/-it. Now, we can distinguish two sub-phenomena:

e/i change: In this case the vowel preceding the ending is e as seen in werf-. The vowels u and i of the ending are close vowels. They "pull" the preceding vowel e up (assimilation). If you move along the "Vokaltrapez"/vowel trapecium starting at e moving towards the close vowels you end up at i. That's why the singular forms have an i and not an e.
In later times, the 1st person singular moved back to the e sound. Additionally, the verb endings got simplified a bit but their influence on the preceding vowel remained. So, today we have:

infinitive: werfen
1st person singular: ich werfe
2nd person singular: du wirfst
3rd person singular: er wirft
1st person plural: wir werfen
2nd person plural: ihr werft
3rd person plural: sie werfen

Umlaut: The second sub-phenomenon is umlaut in 2nd and 3rd person singular. The sound i of the verb ending is a front vowel. If it is preceded by a non-front vowel like a, o or au this vowel is fronted by assimilation. An a getting fronted is an ä (fahren - du fährst), an o getting fronted is an ö (stoßen - du stößt) and an au getting fronted is an äu (saufen - du säufst). The u of the 1st person ending does not yield a fronting. Thus the conjugation of (present-day) fahren is

infinitive: fahren
1st person singular: ich fahre
2nd person singular: du fährst
3rd person singular: er fährt
1st person plural: wir fahren
2nd person plural: ihr fahrt
3rd person plural: sie fahren

  • These two phenomena are not found regularly with weak verbs because (in simple terms) weak verbs had different verb endings than strong verbs.
  • Sometimes the i of e/i change becomes a long one that is written ie (lesen - du liest)
  • Sometimes the e of e/i change has become an ä or ö (gebären - du gebierst; erlöschen - du erlischst)
  • Sometimes there is no umlaut to avoid an ambiguity (saugen - du saugst instead of du säugst since there is a verb säugen).

To answer your question about how to know which verbs show this phenomenon: If you know that a verb is a strong one, then you can assume that there is e/i change or umlaut in 2nd/3rd person singular. You have only to learn by heart those cases where something unexpected happens.


It's the same concept as in the English or French languages, some verbs just are different. Usually the concerned verbs are more commonly used in language and/or of older origin.



Sein: Ich bin, Du bist, Er ist, Wir sind, Ihr seid, Sie sind


To be: I am, You are, He is, We are, You are, They are


être: Je suis, Tu es, Il est, Nous sommes, Vous êtes, Ils sont


I remember several reasons:

  • ancient methods to express grammatical functions (inflection), which remained within the language, but are not productive anymore (singen, sang, gesungen vs. verlinken, verlinkte, verlinkt)
  • highly productive words such as sein, which are used very often and are prone to change
  • phenomena such as the Präteritopräsentia, where preterite forms became present. A similar example is „möchten“, which people do not recognise as Konjunktiv II anymore
  • „wrong” strong inflection, such as schneien - schnie - geschnien, winken - winkte - gewunken; preisen - pries - gepriesen (from preisen, preiste, gepreist)
  • Konjunktiv II has problems in Verbs such as beginnen (begönne or begänne?); this would have been easier in Old or Middle High German, since plural inflection was different

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