In the late fifties, the present writer came to the conclusion that, in all languages of the world, the form of words depends not on two but on three basic factors: regular sound change, analogical change, and irregular sound change due to frequency. The latter implies that very frequently used morphemes, words, or word groups often undergo irregular reductions: *hval-it' - hval-i, *gospodja - gospa, *staru jemu - staremu. There are six arguments which can be mentioned in favour of the theory of irregular sound change due to frequency.
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