Is it possible to draw a border line between ontology and epistemology? A positive answer to this question looks attractive, mainly because it reflects convictions deeply entrenched in our common sense view of the world. However, anyone wishing to clarify the distinction between the ontological and the epistemological dimensions meets problems. This is due to the fact that the separation between factual and conceptual is not clean, but rather fuzzy. It is certainly correct to state that science means to offer correct information about the world, but the extent to which it succeeds in accomplishing this task is always questionable. We cannot claim that the picture provided by today science - our current scientific image of the world - is absolutely correct, because the history of science itself shows us that any such statement is likely to be rejected by future generations. While it may be recognized that science purports to offer a correct description of the real world, the past experience should also prompt us to accept its claims sub condicione, and to view them as merely provisional.