Over the last two decades the traditional conception of intelligence and other mental powers as stable individual assets has been challenged by approaches in psychology emphasising context and "situated cognition". This paper argues that the debate should not be seen as an empirical dispute, and relates it to discussions in philosophy of mind between methodological solipsists and varieties of externalists. In the light of this I argue that attempts to conceptualise the identity over time of mental powers qua individual assets run into intractable difficulties. Hence "individual asset" views of many abilities should be abandoned. Implications for education policy particularly in regard to assessment are explored.