Existing research identifying common student ideas about forces focuses on students' misunderstandings, misconceptions, and difficulties. In this paper, we characterize student thinking in terms of resources, framing student thinking as continuous with formal physics. Based on our analysis of 2048 written responses to conceptual questions, we identify six common conceptual resources for understanding forces. We document context-sensitive patterns in resource activation, and we discuss limitations of our research based on the demographics of our sample.