We present a new account of category structure derived from neuropsychological and developmental data. The account places theoretical emphasis on functional information. We claim i) the distinctiveness of functional features correlated with perceptual features varies across semantic domains, ii) the perceptual features representing specific functional mechanisms are strongly correlated with their function. The representational assumptions which follow from these claims make strong predictions about what types of semantic information is preserved in patients showing category-specific deficits following brain damage. We present a connectionist simulation which, when damaged, shows patterns of preservation of distinctive and shared functional and perceptual information varying across semantic domains. The data model both classic dissociations between knowledge for artefacts and for living things and recent neuropsychological evidence concerning the robustness of functional information.