Educational researchers have explored the importance of performance, recognition, and interest in establishing and maintaining a STEM identity. Research has also demonstrated that the ways students describe themselves and how they participate in STEM communities can provide insight into their role identity salience; however, there has been little work to explore the ontological beliefs of students about STEM people and how this influences their ability to see themselves as possessing a STEM identity. This research explores the ontological beliefs of high school students, with specific attention to the ways in which they describe what constitutes a math person, science person, physics person, or engineer and how these descriptions influence their ability to take on these role identities.