The knowledge problem in social sciences: Epistemic uncertainty

In this paper we deal with the problem of the knowledge under uncertain conditions. Since Plato definition in Teetetos, knowledge has been defined as a true belief and this has been thought as a clear and distinct idea. So, if we have any kind of knowledge, it can't be uncertain. We are trying to show how this point of view changed since fuzzy sets theory has been proposed: it is now possible to define knowledge even in conditions of epistemic uncertainty. This is the point of view we try to explain here.