The relevance of Aristotle's philosophy today is the survival of many Aristotelian concepts, definitions, distinctions, in the culture of many countries. In some cases, e.g. in the fields of logic and of metaphysics, the Aristotelian concepts survive as useful instruments for reasoning, like the concepts of category, contrariety, contradiction, or the distinctions between matter and form and between potency and act. But in other fields, like biology and psychology, some Aristotelian doctrines serve equally as examples of conceptual innovations, as was recognised by the biologist Max Delbrtick about the discovery of DNA and by Anthony Kenny about the discussion of the "Mind-Body Problem." Even in the fields of ethics and of politics, the revival of the practical philosophy of Aristotle has been an occasion for developing new models of social life and organisation of society, as is shown by philosophers like Alasdair MacIntyre and Martha C. Nussbaum, and by economists like Amartya Sen.