 The very idea of combining logic and probability might look strange at first sight (Hájek 2001). After all, logic is concerned with absolutely certain truths and inferences, whereas probability theory deals with uncertainties. Furthermore, logic offers a qualitative (structural) perspective on inference (the deductive validity of an argument is based on the argument’s formal structure), whereas probabilities are quantitative (numerical) in nature. However, as will be shown in the next section, there are natural senses in which probability theory presupposes and extends classical logic. Furthermore, historically speaking, several distinguished theorists such as De Morgan (1847), Boole (1854), Ramsey (1926), de Finetti (1937), Carnap (1950), Jeffrey (1992) and Howson (2003, 2007, 2009) have emphasized the tight connections between logic and probability, or even considered their work on probability as a part of logic itself.