The postdoctoral period is generally one of low pay, long hours, and uncertainty about future career options. To better understand how postdocs conceive of their present and future goals, we asked researchers about their scientific identities while they were in their postdoctoral appointments. We used discourse analysis to analyze interviews with 30 scholars from a research-intensive university or nearby research institutions to better understand how their scientific identities influenced their career goals. We identified two primary discourses: bench scientist and principal investigator (PI). The bench scientist discourse is characterized by implementing other people's scientific visions through work in the laboratory and expertise in experimental design and troubleshooting. The PI discourse is characterized by a focus on formulating scientific visions, obtaining funding, and disseminating results through publishing papers and at invited talks. Because these discourses represent beliefs, they can--and do--limit postdocs' understandings of what career opportunities exist and the transferability of skills to different careers. Understanding the bench scientist and PI discourses, and how they interact, is essential for developing and implementing better professional development programs for postdocs.