In certain cases the difference between consecutive stages of a language may be explained as a change in the system of rules of the grammar of that language (Chomsky & Halle 1968, 249-252; King 1969; Kiparsky 1968). Between consecutive stages a rule may be added, lost, structurally simplified, or reordered relative to the earlier order. Such changes among phonological rules, when phonetically conditioned, represent an increase in grammatical simplicity in a measurable sense (King 1969, 39-63, 65; Kiparsky 1968; Halle 1962).
It has also been recognized that grammatical categories can condition phonological rules. The function of such conditioning appears to be the preservation of surface structure organization defined by grammatical categories, or what Kiparsky has termed “paradigm coherence” (1972, 208). Yet grammatical (non-phonetic) conditioning of phonological rules has been regarded as decreasing, rather than increasing, simplicity (King 1969, 134-139). In this paper I shall be concerned with the historical development of grammatical conditioning on phonological rules, and the role which paradigm coherence, or paradigmatic regularization, plays in grammatical simplification.