 Equally important, and often neglected, is the converse theorem that establishes how you can avoid such a predicament. If your subjective probabilities conform to the probability calculus, then no Dutch book can be made against you (Kemeny 1955); your probability assignments are then said to be coherent. Williamson (1999) extends the Dutch Book argument to countable additivity: if your credences violate countable additivity, then you are susceptible to a Dutch book (with infinitely many bets). Conformity to the full probability calculus thus seems to be necessary and sufficient for  coherence.[5]  We thus have an argument that rational credences provide an interpretation of the full probability calculus, and thus an admissible interpretation. Note, however, that de Finetti—the arch subjectivist and proponent of the Dutch Book argument—was an opponent of countable additivity (e.g. in his 1974). See Hájek (2009c) and the entry on  Dutch Book arguments  for various objections to Dutch Book arguments for conformity to the probability calculus and for other putative norms on credences.