Traditionally the individual "I" is described as a relatively stable entity that is carried from one situation to another. However, a growing body of research has argued for a more flexible approach to identity. This article looks at identity as something situated and transformed in social transaction. The analysis made here examines three aspects of identity formation "disjunctive space", "inter-subjective space" and "ethical space". We study the rhythmic shift between those different identity spaces in six college students' ongoing conversation concerning sustainable development, human freedom, and solidarity. It is shown how identity is constituted in the three different spaces during student discourse. We demonstrate how identity is part of a continuous and contingent inter-human activity, where the interlocutors are constantly forced to answer the question: Who are you? We discuss the consequences of this finding for education for sustainable development. (Contains 2 footnotes.)