 But as Lewis (1983e) makes clear, natural properties play many more roles in his larger philosophy, including in the theory of rationality, the theory of mental content, the theory of linguistic content, and the theory of laws. It is rational to have a belief with a more natural rather than a less natural content. If two different assignments of beliefs and desires would make equally good sense of an agent’s dispositions, the more natural assignment is the correct one. If two different interpretations of the words of a public language would make equally good sense of speakers’ practices, the more natural interpretation is the correct one. And laws are simple generalisations, where simplicity is defined in part in terms of naturalness.