Science education research has built a strong body of work on students' understandings but largely overlooked the nature of science knowledge itself. Legitimation Code Theory (LCT), a rapidly growing approach to education, offers a way of analyzing the organizing principles of knowledge practices and their effects on science education. This article focuses on one specific concept from LCT--semantic gravity--that conceptualizes differences in context dependence. The article uses this concept to qualitatively analyze tertiary student responses to a thermal physics question. One result, that legitimate answers must reside within a specific range of context dependence, illustrates how a focus on the organizing principles of knowledge offers a way forward for science education.