Against inertia

In this paper I question the Inertial Theory of language change put forward by Longobardi (2001), which claims that syntactic change does not arise unless caused and that any such change must originate as an 'interface phenomenon'. It is shown that these two claims and the contention that 'syntax, by itself, is diachronically completely inert' (Longobardi, 2001:278), if construed as a substantive, falsifiable theory of diachrony, make predictions that are too strong, and that they cannot be reduced (as seems desirable) to properties of language acquisition. I also express doubt as to the utility and necessity of a methodological/heuristic principle of Inertia.