 In an effort to provide identity conditions for properties, one could mimic those for sets, or equate the former with the latter (as in class nominalism; see note 3), and provide the following extensionalist identity conditions: two properties are identical iff they are co-extensional. This criterion can hardly work, however, since there are seemingly distinct properties with the same extension, such as having a heart and having kidneys, and even wildly different properties such as spherical and weighing 2 kilos could by accident be co-extensive.