Millikan's discussion of substance concepts in terms of their information-gathering role ignores the analyses of information-based perception and action developed within the tradition of ecological psychology. Her introduction and use without definition of key Gibsonian terms such as “affordance” and “direct perception” leaves those of us investigating such concepts uncertain of the extent to which she appreciates their theoretical importance. Due recognition of the realist account of categorical perception developed by J. J. Gibson would provide mutual benefit to modern externalist philosophy as well as to experimental psychology and to those investigating the ecological approach to perception–action.