 A popular misconception is that Boole’s algebra of logic is the Boolean algebra of classes with the usual operations of union, intersection and complement. This error was forcefully pointed out by Hailperin in his 1981 paper “Boole’s algebra isn’t Boolean algebra,” a theme repeated in his path-breaking book Boole’s Logic and Probability (1986).  Nonetheless the goal of the two algebras, Boole’s algebra and Boolean algebra, is the same, to provide an equational logic for the calculus of classes and for propositional logic.  Thanks to Hailperin’s writings, for the first time there was clarity as to why Boole’s algebra gave correct results. 