Almost any within-word phonological process can apply between adjacent segments in adjacent words. But iterative, long-distance processes like vowel and consonant harmony and stress assignment rarely extend outside the word. Even iterative tonal processes often affect only a single tone in an adjacent word; likewise, the rare cases of grammaticized phrasal vowel harmony extend only one syllable into another word. Why? The phonetic precursors of phonological processes are local, their effects falling off rapidly with distance from the trigger. Becoming iterative requires phonologization of a long-distance process, and phonologization is not facilitated in the infrequent collocations of productive syntactic combination.