Lewis and Rational Inference

What, exactly, is involved in rational inference? Lewis thought that there were three elements: the reception of facts to reason about, the perception of a logical relation, and the arrangement of those facts to draw a fresh conclusion. The link is to a post on DI2 that contains some discussion of what Lewis thought reasoning is, including some material by Peter Williams which makes use of some passages in The Discarded Image, and some passages in Why I am Not a Pacifist.