 Some philosophers will insist that not all of these concepts are intelligible; some will insist that one of them is basic, and that the others are reducible to it. Moreover, the boundaries between these concepts are somewhat permeable. After all, ‘degree of confidence’ is itself an epistemological concept, and as we will see, it is thought to be rationally constrained both by evidential support relations and by attitudes to physical probabilities in the world. And there are intramural disputes within the camps supporting each of these concepts, as we will also see. Be that as it may, it will be useful to keep these concepts in mind. Sections 3.1 and 3.2 discuss analyses of concept (1), classical and logical/evidential probability; 3.3 discusses analyses of concept (2), subjective probability; 3.4, 3.5, and 3.6 discuss three analyses of concept (3), frequentist, propensity, and best-system interpretations.