The purpose of this qualitative study was to identify and explain the origins of physics and chemistry teacher candidates' beliefs about teaching about ethics through socioscientific issues (SSI). This study utilized a series of in-depth interviews, while the participants (n = 12) were enrolled in a 9-month teacher education program at an urban university in Canada. Our data analysis revealed that beliefs about teaching physics and chemistry using SSI derive from a complex web of fundamental beliefs exemplified by four "archetypes" representing the subject-specific identities of our teacher candidates--Model Scientist/Engineer, Model Individual, Model Teacher, and Model Citizen. Furthermore, we found that the justification for belief change required by a particular teacher candidate depends on these subject-discipline identities. Thus, the presence of each archetype in preservice classrooms has ramifications for the way a teacher educator should encourage his or her students to include SSI in their teaching. (Contains 3 tables, 3 figures, and 5 notes.)