The debate on rationality of science go round the influence of external factors {psychological, sociological, political and religious) on the development of scientific theories. All models of scientific change analyse the relationship between external and internal factors. The aim of this paper is to explain the role played by the external factors in models of scientific change. Fist of all, I look over the models of T. Kuhn, I. Lakatos and L. Laudan, expounding their characterization of external factors. Secondly, I show several historical cases, where one can see the influence of external factors in the development of science, and I analyse them from externlist and internalist positions. Finally, I propose to incorporate the external factors in a new perspective of models of scientific change out of externalist position
