As a member of the Germanic family of languages, Yiddish would be expected to exhibit a fundamentally Germanic sound structure. The most salient characteristic of German phonology may be the strong tendency to place the accent of a word on the root syllable which is often the first syllable of the word. A related Germanic characteristic is the tendency for vowel length distinctions to be expressed on the stressed syllable.
The sound structure of a language is the way in which the speakers of the language analyze speech sounds. An indirect way to observe this is through the way the speakers interpret words from other languages. This can be seen in the way loanwords are modified when they are assimilated into the language.
These principles underlie Daniel Leibel's study "On Ashkenazic Stress" whic appeared in 1965 in the Second Collection of "Field of Yiddish" edited by Uriel Weinreich (Mouton, the Hague). Leibel begins by noting that, in Yiddish, it is rare to stress Hebrew words on the final syllable although final syllable stress in the usual pattern in Classical Hebrew. He goes on by saying that a majority of authors have claimed that the general pattern in Yiddish is to stress Hebrew words on the next to last syllable, the penultimate.
Given the generalization that Hebrew words in Yiddish are stressed on the penultimate, various theories have been put forward to explain why this should be so; that it represents an influence of Polish on Yiddish, that it is an inheritance from a pre-Yiddish form of Hebrew that was already stressed on the penultimate or that it represents a conequence of the supposed loss of distinctive length in Yiddish.
All of these theories, Leibel shows, are defective. Their most serious problem is that Hebrew words in Yiddish are not essentially stressed on the penultimate. They are stressed on the first syllable. This is not immediately clear for the largest number of words which have two syllables since the first syllable in these words is also the penultimate syllable. But the situation can be clarified by looking at words of three syllables. In these words stress also occurs on on the first syllable except in cases where the first syllable has a short vowel and a following syllable has a long vowel. In the latter case the stress is does fall on the penultimate.
Leibel explains these facts by noting that German places the stress on the root syllable of a word which is generally the first syllable. When German borrows words it treats the first syllable of the loanword as a root and stresses it. The exception is when a borrowed word has a long vowel in a later syllable. German does not have long vowels in unstressed syllables. In some cases German deals with this by shortening the long vowel but in other cases it preserves the long vowel and moves the stress to that syllable.
Leibel assumes that Yiddish is a close relative of German and behaves in the same way. In the case of Hebrew loanwords it generally treats the first syllable as if it were a root and stresses. Where a Hebrew word has a long vowel in a later syllable that sylable, which may be the penult, gets the stress.
Leibel's analysis stands out from that of other linguists in several ways. One is that he saw the Hebrew words that were borrowed into Yiddish as coming into Yiddish with distinctive long and short vowels. Most of the linguists who had looked at the Hebrew material in Yiddish, notably, Solomon Birnbaun, Jechiel Bin-Nun, and Max Weinreich had accepted the opinion of specialists in Hebrew linguistics that the Hebrew which was the source of Yiddish borrowings did not have distinctive vowel length. Later, however, Dovid Katz was to support Leibel in this. Another difference, is that other linguists have generally seen the pattern of vowel length in the Hebrew words and the stress pattern as having related causes. Birnbaum, Bin-Nun, and Weinreich attributed all these features to the influence of the Germanic system while Dovid Katz saw them all as being inherited from an earlier form of Hebrew. Leibel, as we have seen, attributed distinctive vowel length to the Hebrew source and the change in stress to Germanic influence.
In Leibel's time, the descent of Yiddish from German was virtually unquestioned. This is no longer true as Paul Wexler has presented the theory that Yiddish is a relexified Slavic language. Leibel's argument is strong support for the originally Germanic character of Yiddish. However. the tendencies toward initial stress and toward expressing length distinctions on a stressed syllable are not just features of German but are shared by all the Germanic languages. Leibel's argument can also be used to support the descent of Yiddish from another Germanic language.