 All non-relativist philosophical systems acknowledge substances in the most generic sense of that term, for that is only to acknowledge that there are some fundamental entities in their system. Most, if not all, philosophers acknowledge that we cannot function without using substance concepts in the narrower sense, for the notion of an enduring particular or individual substance is essential to our making sense of the world as we live in it. But three things at least remain controversial. First, it is disputed what kinds of concepts need to be deployed to characterise these enduring things: are they the rich variety of traditional or ‘Aristotelian’ substance concepts, or will various ways of identifying things simply as physical bodies with certain characteristics do the job? Second, it is still unclear how far our substance concepts purport to reflect a component in reality (real or imagined) over and above the bundle of properties that constitute its intelligible aspects. Third, the unclarity of the connection between what a thing is and what it does leaves unresolved the degree of interdependence between substance concepts and notions of purpose and final causation.