This paper describes the philosophical conditions for a "Design Theory". A theory of design is a theory that recognises a mode of reasoning that produces the new. There is a massive gap between the traditional Philosophy and the Design Theory. Nevertheless, in the current context philosophy is modifying itself and can invent new relationships with the concepts of the design theory. The introduction of the notions of fiction, interdisciplinary site, genericity, enables opening spaces in which we can address heterogeneities. Classical scientific and philosophical disciplines are no longer able to describe these and Design can treat them with the idea of "new". These relationships between Philosophy and Design are developed in an example, the creation of Genetically Modified Organism Fish. We show that it is not a complex object, but an integrative one, which implies new methodological approaches, participating to philosophy and to design theory together.