While in the experimental sciences, statistical probability is almost exclusively discussed, influential Bayesians in philosophy understand probability in a subjective sense of rational degrees of belief, whereas the third group of mathematical probability theorists ignores this interpretational conflict. This book argues that both concepts of probability are necessary, which is why a dualistic approach is developed that aims to establish bridging principles between the two concepts of probability. Drawing on a well-known passage from Kant, the dualistic position can be formulated as follows: Subjective probability without statistical probability theory is blind, while statistical probability without subjective probability theory is empty. However, the dualistic position does not mean that.