 Subjective probability theory, often going under the sobriquet ‘Bayesianism,’ is by far the dominant paradigm for modeling partial belief. The literature on the subject is by now very large. The summary provided here will, of necessity, be rather brief. For an article-length introduction see the entry on  Bayesian epistemology,  Easwaran (2011a, 2011b) or Weisberg (2011). For a book-length introduction see Earman (1992), Skyrms (2000), Hacking (2001), Howson and Urbach (2006) or Huber (2018). For an article-length introduction to Bayesian models of rational choice, see the entry on  decision theory.  For an approachable book-length introduction to the theory of rational choice see Resnik (1987).