 Dynamic rationality is dealt with in some detail in “Dynamic Rationality: Propensity, Probability, and Credence” (1988b [2005]). This kind of rationality revolves around the tenet that rational action must obey the maxim: Respect the frequencies. For it to be accomplished, credence, or the degree of conviction leading to action, must be empirically informed, namely it should take into account objective facts. Salmon holds that explanation has a crucial role in that connection because causal knowledge of phenomena provides the optimal basis for action. The notion of propensity is deemed no less fundamental and is assigned the purpose of bridging the gap between objective probabilities, namely frequencies, and personal probabilities on whose basis people act. Personal probabilities should not be construed in a subjective sense, not only because for Salmon subjectivism is not an admissible interpretation of probability  (§ 2.3),  but more generally because subjective opinions cannot be taken to offer good grounds for rational action. Rational action can only be based on rational degrees of conviction, the emphasis being on rational as opposed to merely subjective.