Some recent work has argued that agreement and case-assignment dependencies between a functional head and a nearby NP are not part of the syntactic derivation proper, but take place in the postsyntactic, morphological component of the grammar. I argue that this view is correct, by showing that one of its largely unexplored predictions has real empirical payout. The prediction is that the dependency-forming properties of functional heads, being morphological in nature, are mutable, and may be conditioned by nearby roots and functional structure. I focus here on Voice heads in Choctaw, and my starting assumption is that, by default, $ {\mathrm{Voice}}_{\left[+\mathrm{N}\right]} $ (the Voice head which introduces a specifier) agrees with its specifier (the external argument) and $ {\mathrm{Voice}}_{\left[-\mathrm{N}\right]} $ (i.e. specifier-less Voice, found in unaccusatives) does not agree with anything. However, I propose that in some environments, $ {\mathrm{Voice}}_{\left[-\mathrm{N}\right]} $ does launch a $ \phi $-probe, and it results in $ {\mathrm{Voice}}_{\left[-\mathrm{N}\right]} $ agreeing with the internal argument. I refer to these configurations as ‘low ergatives’. A small survey of previous work on case and agreement dependencies suggests (a) that the case-assignment properties of functional heads are mutable in the same way, and (b) that the reverse is attested – in some environments $ {\mathrm{Voice}}_{\left[+\mathrm{N}\right]} $ fails to launch a $ \phi $-probe. This is consistent with a purely morphological model of agreement and case-assignment: just as the exponence and interpretation of functional heads can be conditioned by adjacent roots and functional material, so too can the dependency-forming properties of those heads be conditioned in the same way.