‘Truth in Fiction’ is a celebrated paper in the analytic tradition on the nature and function of fiction. Lewis published the paper in the American Philosophical Quarterly in 1978 (vol. 15). But, as his correspondence reveals, the gist of his theory of fiction occurred to him well before 1978. In this letter to Kendall Walton, he explains the history of the paper (to date) and its life as a section of his 1973 book Counterfactuals. He also mentions that he needs to respond to Kripke’s thesis that a fiction entity, say, a unicorn, exists at no possible world. What we find is that Lewis adopted his view of fiction earlier than one might think. Indeed, this is one instance among many where he adopted a view early on in the 1960s and spelled it out later. To use another example: Lewis published his theory of time travel in 1976 (‘The Paradoxes of Time Travel’, American Philosophical Quarterly) but wrote the descendant of the paper in 1970 and gave informal lectures on time travel in 1969. When trying to understand the origins and development of Lewis’s thought, we discover that he adopted many of his views early on in the 1960s and later at various points in his career spelled them out or finished off what would be the published version. We can infer (after identifying other cases of this kind) that he arrived at most of his philosophical positions by 1970 and spent the rest of his career articulating, refining, and defending them.