In this dissertation I aim to clarify the concept of probability. There are three kinds of interpretation of probability: the objective interpretation, the logical interpretation, and the subjective interpretation. The objective interpretation understands probability as a natural property that exists independently of our minds. I will clarify and defend one version of objective probability—the propensity interpretation of probability. I reject the logical interpretation of probability that treats probability as a logical relation between evidence and hypothesis, and maintain that probability is an empirical relation. The subjective interpretation of probability, which is quite influential in recent literature, understands probability as the...