A scandalous matter now forgotten, even among historians of philosophy, the "Leslie affair" may be a turning point of some significance in the debates over causation in Anglophonic philosophy. John Leslie (1766 - 1832) was a Scottish mathematician and physicist. In 1804 he published a book on the nature and properties of heat that earned him some favorable attention among the cutting edge scientists of the day. In 1805 the University of Edinburgh decided to make him professor of mathematics. BUT ... there was surprising kickback from church officials on the ground that Leslie had said positive things about David Hume and about Hume's understanding of causation as the mere fact of constant and invariable sequence. The establishment saw this notion as a danger to the accepted religion, and specifically to any cosmological argument for the existence of God as a First Cause. Causation has to mean something, some REASON WHY some sequences are invariable, f...