At the core of David Lewis’ philosophical outlook is the doctrine of Humean supervenience. According to this doctrine, as he says in the Introduction to Philosophical Papers II, ‘all there is to the world is a vast mosaic of local matters of particular fact, just one little thing and then another. (But it is no part of the thesis that these local matters are mental.) We have geometry: a system of external relations of spatiotemporal distance between points. Maybe points of spacetime itself, maybe point-sized bits of matter or aether or fields, maybe both. And at those points we have local qualities: perfectly natural intrinsic properties which need nothing bigger than a point at which to be instantiated. For short: we have an arrangement of qualities. And that is all. There is no difference without difference in the arrangement of qualities. All else supervenes on that’ (1986, ix-x). In this letter of the month Lewis clarifies what he meant by the clause ‘just one little thing and then another’ and reacts to the suggestion that his use of ‘Humean’ in the phrase ‘Humean supervenience’ is not appropriate because Hume did not endorse any ontological thesis that denies, as Galen Strawson says, ‘any necessary connection or causal influence in concrete reality’ (”Humeanism”, Journal of the APA, 2015, vol. 1, no. 1, p. 96). (© Estate of David K. Lewis.)