Abstract In the first half of the 20th century following the Neogrammarian tradition, most researchers believed that sound change was always conditioned by phonetic phenomena and never by grammar. Beginning in the 1960s, proponents of the generative school put forward cases of grammatically conditioned sound change. From then until now, new cases have continued to come to light. A close look at the development of intervocalic ‐s‐ in Greek, reveals the divergent approach of the two schools of thought. All examples of grammatical conditioning are amenable to explanation as some combination of regular sound change, analogy, or borrowing. Neither the Neogrammarian belief in exceptionless phonetically conditioned sound change nor the generative inspired belief in grammatical conditioning is a falsifiable hypothesis. Because of its assumptions are more parsimonious and its descriptive power more subtle, the Neogrammarian position is the more appealing of these two equally unprovable doctrines.