That language contact, especially of a long-standing variety, can influence the historical development of the contacting languages, has been established in the literature on the subject (for a recent, comprehensive summary, see Hock 1986:380–531). In fact, it has been said that such contact can lead to a tendency for the involved languages “to streamline … and thus render uniform to a considerable degree their overall shared typological profile” (Birnbaum 1985:2). Linguists have also theorized about the question what might constitute a possible contact-induced change, based no doubt upon the observation that certain rules, constructions, or parts of the vocabulary lend themselves more easily to borrowing than others. Thus, Jakobson ([1938] 1949:359) maintained that “la langue n’accepte des éléments de structure étrangers que quand ils correspondent à ses tendences de développement.” And, similarly, Weinreich (1964:25) attributed any foreign influence to a “trigger effect, releasing or accelerating developments which mature independently.” This idea of a language being internally prepared for contact-induced change does not exclude the possibility that items or rules can be borrowed without such a motivation, a phenomenon that seems to be more common than allowed in previous theoretical, especially functional frameworks (Weinreich, Labov and Herzog 1968:155–165).
Sorbian, a Slavic-language enclave in Germany, with few direct contacts with other Slavic languages since the sixteenth century, would seem to be a prime candidate for streamlining parts of its grammar with that of the adjacent and co-territorial dialects of German. Conversely, the lengthy contact between Sorbian and German cannot have left the German dialects, dominant as they seem to be today, completely untouched. Obviously, we must examine those changes in Sorbian that either did not occur at all in any of the other Slavic languages, or that have been reported to be due to German influence in these other Slavic languages as well. And, for possible Sorbian influences in German, the linguist must determine whether such changes occurred in other German dialects far removed from the Sorbian language area.
In the first category, i.e., suspected German-induced change in Sorbian, there is (1) the phenomenon of umlaut (also assumed for Czech); and (2) the development of a definite article (also reported in Czech but developed systematically in Bulgarian and Macedonian as well). In the second category, i.e., suspected Sorbian-induced change in German, there is (3) the neutralization of vowel length in New Lusatian, a dialect of East Central German in the Sorbian language area (also reported in western dialects of German bordering on Romance, but also in less peripheral dialect areas; see Wiesinger 1983:1088–1101); and (4) the rise of voice assimilation across the morpheme boundary in New Lusatian (not reported elsewhere in the German language core area).
Of these contact phenomena, only (2) and (4) seem to merit the status of contact-induced changes (see also Schaarschmidt 1983 and 1997:156, respectively). For (1), the chronology and conditions of umlaut in Sorbian differ substantially from those in German, while (3) appears to be an instance of a universal tendency to eliminate binary quantity distinctions.