In this article we report on a group activity, based on previous work [Hansson & Redfors: 2006b, "Science & Education" (accepted)], in an upper secondary physics class in Sweden. The aim was to engage students in a discussion about which presuppositions that are really necessary for physics. During the activity the students were to decide about the physics' view concerning a number of statements. The overall aims of the study were to gain more knowledge about what kind of presuppositions the students associate with physics, and to identify possible ways to address this with students in class. The study shows that it is common for students to associate scientism' with physics. This is only to some extent problematised and questioned during the discussions. Furthermore we can see that presuppositions necessary for physics are not immediately recognized by the students.