Forecasting of ethnolinguistic vitality can only be done within a well-functioning descriptive and explanatory model of the dynamics of language stability and shift. It is proposed that the Perceived Benefit Model of Language Shift, used with a taxonomy of language shift motivations, provides that model. The model, based on individual language choice decisions which are motivated by the speaker's perceived personal benefit, is first explained. The model is then validated through case studies by demonstrating how the motivators which were present in the past would have predicted the language vitality scenarios that actually developed. The possibility of extending the change model beyond language choice is examined. The effectiveness of the model points to observable language use and language attitude patterns as the most important predictors of ethnolinguistic vitality. (Contains 1 figure.)