There are common words in Germanic languages that have a long "o" vowel in the stem, and which in modern German seem to be either "o" or "au" randomly. Examples:

Dutch ROOD, Swedish RÖD, German ROT

DUTCH DOOD, Swedish DÖD, German TOT

but: Dutch KOPEN, Swedish KÖPA, German KAUFEN

Dutch LOPEN, Swedish LOPP (noun), German LAUFEN

Is there a rule, or is it random? And what is the reason (maybe high vs. low German)?


2 Answers 2


In Proto-Germanic (PG) the prototypes of all the four words had the diphthong /au/ in the root:

rot < PG *raudaz

tot < PG *daudaz

kaufen < OHG noun koufo (“merchant”) < Latin caupō (“tradesman, shopkeeper”)

laufen < PG *hlaupaną

During the transition from Proto-Germanic to Old High German the diphthong /au/ > /ô/ before /r/, /h/ and all dentals, otherwise /au/ > /ou/. Since in *raudaz and *daudaz the diphthong /au/ was before the dental /d/, /au/ > /ô/, in *hlaupaną it was before /p/, so this change didn't happen. The exact PG form the Latin caupō transformed into is unknown to me, anyway /au/ was not before a dental there, so Latin /au/ > OHG /ou/.

Dutch has /oː/ in all the four words, because in its ancestor language Old Saxon aka Old Low German, the Proto-Germanic diphthong /au/ consistently developed into a long vowel /oː/.

As for Swedish, I don't know Old Norse and the Scandinavian languages enough to comment competently on the vowel change they had, maybe someone else here can do that.

  • Thanks a lot! By the way, do you mean "Old Saxon aka Old Low German"? Otherwise I don't understand that part :)
    – geodude
    Jan 7, 2015 at 8:59
  • The ancestor of Dutch is actually Old Frankish or Old Low Franconian, but the point is valid nonetheless. Jan 7, 2015 at 9:26
  • As for Swedish, it borrowed heavily from Hansa-Low German in the middle ages, so that may be an explanation. Jan 7, 2015 at 9:28
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    @geodude - Well, the PG *au > OE eo, all the 4 words had this eo in the Old English times. They split in the Middle English period, when in some of the words this eo got shortened to e, and in some other words it turned into øː > . This shortening was inconsistent according to some sources, or happened before t, d, th acording to the others. Anyway, the ME e remained /e/ in ModE (red, dead), the ME became ModE /iː/ (cheap, leap). The shortening is mentioned here: en.wikipedia.org/wiki/Middle_English_phonology , just search for 'dead' on that page.
    – Yellow Sky
    Jan 7, 2015 at 16:17
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    @geodude A quick lookup on Icelandic gave me "hlaupa", interestingly enough... Jan 8, 2015 at 8:59

“Rot” and “tot” have a long ō in Old High German, but “laufen” and “kaufen” have the diphthong ou in OHG. ō and ou merge in some languages, in others they go their separate ways.

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