We report on a case of morphological change in progress that falls within the scope of Greek grammatical gender. We interpret gender-related variation of Modern Greek feminine nouns in terms of cognitive and usage patterns, i.e. prototypicality and frequency. Our basic claim is that the observed masculine gender assignment to [+ learned] feminine nouns in <i>-(o)s</i> reveals the shifting boundaries of the specific inflection class and reflects the way in which linguistic use is imposed on linguistic structure through self-regulation. In order to investigate the motivation and the diffusion of the reported gender change, we focus on the use of individual nouns with overlapping gender assignment in written electronic data. The data analysis suggests that (i) gender change is motivated by prototypicality, strengthened by phonetic similarity, and consolidated by high frequency of use, and (ii) gender mobility is explicitly observed in specific text categories characterized by [– learned] style and informal context.