Intragroup behavioral variation defies the explanatory power of the concept collective identity in the study of social movements and collective action. This paper investigates notions of identification and explains the reason why Hardinian identification - as an individual's commitment to a particular group or to his selves over time - is a pow- erful conception to analyze an individual's motivation to act for group interests. It points out that an individual's Hardinian group identifica- tion is a subset of his Hardinian personal identification. It also argues that an individual's epistemological background on interest and interest calculation fundamentally aects his Hardinian identification.