The focus of XXth. Century epistemological concern is the foundation of Social Sciencies, understood as "Sciences endowed with ambiguity" in a double meaning: the possibility of producing their own theoretical object, and the fluctuation between what is ontologically (scientifically) produced and the "ontically" given ideology. At closer range, the problem is to be set in terms of the relationship between Science and Ideology. In order to better understand the foundation of Social Sciences, two levels are to be analyzed: a) negative-critical: the given "ontical" Ideology is lead to crisis, thus paving the way to replacement by Scientific Theory; b) positive-constructive: the actual production of the formal object (ontologic) or, as it were, the transformation of objects made "opaque" by Ideology, into "transparent" ones. In other words, Ideology sets a frame, fencing in the production of concepts and becoming thus the main "epistemological obstacle", in the way of scientific production. Still other epistemological obstacles are slowing down or jeopardizing the construction of Social Sciences, such as: a) intellectualism, contending the entire explanation of phenomena is to be found within the theoretical discourse and its deductive development; and b) naturalism, asserting the same but in reference to its inductive discurse. Only by means of critical examination of epistemological obstacles, and by leading to crisis the "ontically" given Ideologies, the possibility of scientific production is open.