 Perhaps the most distinctive of the roles naturalness plays for Lewis is the theory of mental and linguistic content. This role is sometimes gestured at by saying that natural properties are “reference magnets” (an expression borrowed from Hodes  1984):  the more natural a property it is, the easier it is for thinkers to end up referring to it (or expressing it or thinking about it). Reference to natural properties is something that happens “by default”; the less natural a property is, the more specific and finely-tuned the conditions required to refer to it.