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 (1978) argues that they should be collapsed with the -2 series, leaving only 13 in the -3 series. Some dialects have final consonant devoicing. Merger of into was common in Litvish Yiddish in previous generations. Known as Sabesdiker losn, it has been stigmatized and deliberately avoided by recent generations of Litvaks. Development of "neutral" form As with many other languages with strong literary traditions, there was a more or less constant tendency toward the development of a neutral written form acceptable to the speakers of all dialects. In the early 20th century, for both cultural and political reasons, particular energy was focused on developing a modern Standard Yiddish. This contained elements from all three Eastern dialects but its phonetic attributes were predominantly based on Northeastern pronunciation. A separate article describes the resulting modern Standard Yiddish phonology, without detailing the phonetic variation among the three contributing dialects or the further distinctions among the myriad local varieties that they subsume. A useful early review of the differences between the three main Eastern dialects is provided by the Yiddish lexicographer Alexander Harkavy in a Treatise on Yiddish Reading, Orthography, and Dialectal Variations first published in 1898 together with his Yiddish-English Dictionary (Harkavy 1898). A scanned facsimile is available online. The relevant material is presented there under the heading Dialects. Standardization controversy Harkavy, like others of the early standardizers, regards Litvish as the "leading branch". That assertion has, however, been questioned by many authors and remains the subject of keen controversy. YIVO, the Jewish Scientific Institute, is often seen as the initiating agent in giving phonetic preference to Litvish, but Harkavy's work predates YIVO's and he was not exclusively describing personal preference. A broad-based study provided in the Language and Cultural Atlas of Ashkenazic Jewry (discussed in detail below under the heading Documentation) provides a clearer picture of the more recent YIVO perspective. The heart of the debate is the priority given to the dialect with the smallest number of speakers. One of the alternative proposals put forward in the early discussion of standardizing spoken Yiddish was to base it on the pronunciation of the Southeastern dialect, which was the most widely used