Differential time stability in categorial change

Change affects different parts of the lexicon and grammar differently, and in particular some parts are more time-stable than others. The creation of family names from words of other classes is an example, and many such examples need to be examined before credible generalizations can be made about differential time stability in historical linguistics. In German, the language used here for illustration, family names typically derive from common nouns or adjectives designating the origin, place of residence, occupation, or salient personal characteristics of the families or their heads originally given those names. Despite such origins in nouns or adjectives, and despite retaining the phonology and partly also the syntax of their origins, family names in contemporary German have subtly, but comprehensively, severed ties with their ancestral word classes in their morphology upon attaining name status. This is shown for inflection as well as derivation, and this result renders the traditional word class categorization of family names as a type of noun in languages such as German untenable. Diachronic conclusions are drawn on this basis as to the transience of semantics-pragmatics and morphology on the one hand and the pertinacity of syntax and phonology on the other in category-changing developments of this kind, with other kinds of developments apparently showing different kinds of developmental dynamics.