This paper analyses the use of Polish achievements with durative expressions of godzinę (in an hour) and przez godzinę (for an hour) – types, their use in the progressive and finally a possible relationship between this use and the terminative recategorisation of imperfective achievements. In the analysis we have accounted for a number of linguistic and contextual factors that influence the possibility of the progressive use of achievements. This has allowed us to propose several subclasses of achievements that may undergo recategorisation under specific conditions set in the concluding section.