the vowel /o/, descended from Proto-Yiddish */a/. The first digit indicates Proto-Yiddish quality (1-=*[a], 2-=*[e], 3-=*[i], 4-=*[o], 5-=*[u]), and the second refers to quantity or diphthongization (−1=short, −2=long, −3=short but lengthened early in the history of Yiddish, −4=diphthong, −5=special length occurring only in Proto-Yiddish vowel 25). Vowels 23, 33, 43 and 53 have the same reflexes as 22, 32, 42 and 52 in all Yiddish dialects, but they developed distinct values in Middle High German; Katz (1987) argues that they should be collapsed with the −2 series, leaving only 13 in the −3 series. Comparison with German In vocabulary of Germanic origin, the differences between Standard German and Yiddish pronunciation are mainly in the vowels and diphthongs. All varieties of Yiddish lack the German front rounded vowels and , having merged them with and , respectively. Diphthongs have also undergone divergent developments in German and Yiddish. Where Standard German has merged the Middle High German diphthong ei and long vowel î to , Yiddish has maintained the distinction between them; and likewise, the Standard German corresponds to both the MHG diphthong öu and the long vowel iu, which in Yiddish have merged with their unrounded counterparts ei and î, respectively. Lastly, the Standard German corresponds to both the MHG diphthong ou and the long vowel û, but in Yiddish, they have not merged. Although Standard Yiddish does not distinguish between those two diphthongs and renders both as , the distinction becomes apparent when the two diphthongs undergo Germanic umlaut, such as in forming plurals: The vowel length distinctions of German do not exist in the Northeastern (Lithuanian) varieties of Yiddish, which form the phonetic basis for Standard Yiddish. In those varieties, the vowel qualities in most long/short vowel pairs diverged and so the phonemic distinction has remained. Yiddish has some coincidental resemblances to Dutch in vowel phonology, which extend even to orthography, such as Dutch ij versus Yiddish tsvey judn, both pronounced /ɛɪ/; and Dutch ui (pronounced /œy/) versus Yiddish vov yud (/ɔj/). For example, the Yiddish "to be" is זיין, which orthographically matches Dutch zijn more than German sein, or Yiddish הויז, "house", versus Dutch huis (plural huizen). Along with the pronunciation of Dutch g as /ɣ/, Yiddish is said to sound closer to Dutch than to German because of that even though its structure is closer to High German. There are consonantal differences between German and Yiddish. Yiddish