Preliminary Remarks: Before entering into the subject matter of the paper, it may be useful to present American readers with a sketchy outline of present-day European philosophy of science, as it appeared to me at the International Congress of Philosophy of Science, held in Paris at the Sorbonne on October 15–22, 1949. The sections of which I can give a first hand impression and which are of particular interest for our subject, are those of physical science and of probability.