Pierre Rétat : Luxury. On a superficial view, the debate on luxury which runs through the 18th Century can be seen as a reversal of the theory which saw luxury as an economic stimulus (in mercantilist theory), replacing it by one which saw it as an economic brake (in the Physiocratic and Smithian view of an economy of production). But the notion must also be seen in the context of the ambiguous status of economics, which was still closely associated with morality, politics and philosophy ; luxury is therefore associated with the passions, nature and happiness. The study of luxury in the 18th Century thus throws light on how difficult it was for economics to become a separate field of study.