In this article Strange offers only her second explicit excursion into the epistemology of international theories, the first being a similar section in **States and Markets (1988)**. She argues that theories must be more than description, taxonomy, importation of models from other disciplines or quantitative and that theories must explain some aspect of the international system not obvious to 'commonsense'. In addition she argues for her own version of non-positivism stressing only that rationality of explanation is required for a theory to be scientific. In the second part of this article Strange argues for a non-territorial theory of imperialism based on her four structures of power. The transnational empire she identifies is centred on the 'court' in Washington DC, and she argues that new studies of empire are needed to understand this new type of transnational empire. What is required is a problem solving theory for such an empire, since it is manifestly in existence.