The basis of property rights is a central problem in political philosophy. The core philosophical dispute concerns whether property rights are natural facts, independent of human conventions. In this article, we examine adult judgments on this issue. We find evidence that familiar property norms regarding external objects (e.g., fish and strawberries) are treated as conventional on standard measures of authority dependence and context relativism. Previous work on the moral/conventional distinction indicates that people treat property rights as moral rather than conventional (...) (e.g., Dahl & Waltzer, 2020; Nucci & Turiel, 1993; Tisak & Turiel, 1984). However, these studies explicitly assume that one person owns property that another steals. Study 1 explores judgments of authority dependence regarding ownership in cases that explicitly appeal to stealing and prior ownership as compared to cases that omit such explicit appeals. We find that participants tend to treat ownership as authority dependent when explicit appeals to stealing are absent, but not when the explicit appeals are present. Study 2 examines intuitions about authority dependence of ownership violations as compared to canonical conventional and harm-based moral violations. We find that ownership violations are treated as more authority dependent than harm-based moral violations. This all suggests that some central property norms are treated as conventional. However, we also find that the conventionality of property norms is restricted in several ways. In study 3, we find that people do not treat norms of self-ownership as conventional. Other people cannot take your hair or skin cells even if the teacher says it's okay. Study 4 uses a measure of context relativism to examine the conventionality of ownership norms, comparing different possible norms of ownership. We find that participants regard takings that are violations in their own culture as permissible in other cultures; however, only some foreign norms are deemed acceptable. In study 5 we find another limitation – participants think it's impermissible to take resources from someone based on a new property norm that is retrospectively imposed. Finally, in study 6 we explore whether some takings might be judged to be morally (non-conventionally) wrong as a function of scarcity. We find that when asked about another culture that allows taking, participants tend to say that taking a food item from the person who caught it is permissible when the food is plentiful, but not when the food is scarce. (shrink)