The present article is written by a theoretical physicist who, for some time, has endeavored to trace the origin of the concepts and principles of quantum theory to an empirical background broader than that afforded by delicate optical and mechanical experiments on a microphysical scale involving the microconstant h. In particular he tried to reduce the dominant role of probability in modern physics to irrefutable evidence of a quite general nature. As long as quantum probability is deduced from experience with seemingly uncontrollable micro-mechanisms—think of radioactive disintegration as the most typical example—there will always be the objection that one day we still may find a hidden causality behind those small scale gambling devices called atoms, although one example of an exactly predictable atomic event would make present-day quantum theory untenable. In order to dislodge the remaining classicists from their fortress of doubt one may try to show that quantum probability is not an alibi for a temporary impotence of predicting microphysical events, but is a positive conclusion drawn from experience of a most general type, namely, from the principle of continuity, the basic tenet of the philosophy of Leibniz.