According to Donald Davidson, “what a fully informed interpreter could learn about what a speaker means is all there is to learn; the same goes for what the speaker believes” (Davidson 1983, 148). This is a foundational claim about the nature of semantic properties: these are evidence-constituted properties. They are determined by the principle of charity on the basis of data about the behaviour of the speaker(s). But what exactly is the role of the interpreter in the Davidsonian account of meaning determination? Is she merely a dramatic device or an essential element of the metaphysical picture? In this paper, I investigate whether we can get help in answering these questions from David Lewis’s (1983) distinction between natural and unnatural properties.