 At first blush, best-systems analyses seem to score well on our criteria of adequacy. They are admissible by definition: chances are determined by probabilistic laws (rather than by those expressed by some other formalism). One could in principle ascertain values of probabilities, since they supervene on what actually happens in the universe (though ‘in principle’ bears a heavy burden). Applicability to frequencies is secured through the role that ‘fit’ plays. Schwarz (2014) offers a proof of the Principal Principle, which could be taken to undergird the best-systems analyses’ applicability to rational beliefs and rational decisions. And we have just mentioned the interpretation’s applicability to science. 