 Various explanations have been given as to why Boole could not comprehend the possibility of Jevons’s suggestion. Boole clearly had the semantic concept of union—he expressed the union of \(x\) and \(y\) as \(x + (1-x)y\), a sum of two disjoint classes, and pointed out that the elements of this class are the ones that belong to either \(x\) or \(y\) or both. So how could he so completely fail to see the possibility of taking union for his fundamental operation + instead of his curious partial union operation?