Spirantization and the 7-to-5 vowel merger in Bantu, in Sound Change

Many Bantu languages have the balancée!seven-vowel system i i E a o u u.It is the system that one would, on internai évidence, reconstruct for proto-Bantu.Many other Bantu languages have a reduced five-vowel system i e a o u.The five-vowel Systems are historically almost always the result of a merger of the two highest front and back vowels, respectively; i.e., the result of a merger of *i /*i and of *u/*u ("7>5").Another widespread sound change occurring in Bantu is the one here called "Spirantization".It occurs in seven-vowel languages and affects obstruents in the environment preceding the high vowels i and u (not i and u).It typically créâtes strident fricatives (s, f...) not formerly present in the system.Some remarkable observations can be made concerning the historical co-occurrence of the two sound shifts.Spirantization and 7>5: (i) No language has undergone 7>5 but not Spirantization; (ii) Only few languages have undergone Spirantization but not 7>5.(iii) In languages which have undergone both sound shifts, Spirantization always preceded 7>5.In this contribution I try to "explain" these patterns of co-occurrence without appeal to structuralist chain analyses.I consider both changes as being independently well motivated, and while admitting the possibility that the phonological System äs such may favour or disfavour certain changes I argue that areal norm and areal spread are thé major reasons for thé widespread combined occurrence of Spirantization and 7>5, in that (apparent) order.