The purpose of the present exploration is not to deal with the details of Fleck's analysis of the scientific fact and its conceptual components. The purpose is rather to point to some trend in modern philosophy — as a matter of fact formulated at the time of Fleck's writing of this major book — without assuming that Fleck was aware of those trends and their affinity with his own 'style of thinking". Hence we can say that we are concerned with the whole notion of "Pre-ideas " (Prä-Ideen) as formulated¹ in several major philosophical presentations, or to take advantage of a historical expression -we are interested in the "climate of opinion" in which or against which Fleck's theory was formulated. To be sure, when Whitehead uses the term "climate of opinion" he points to the understanding of the antecedents of a certain world-view.² We are more concerned with the contemporary points of view than with that which preceded Fleck. One could say that we are interested in the contemporary milieu, in the philosophical sense, of Fleck's position and its major issues.