Boole's Chapter XV: Syllogism Details

Abstract

In Boole's famous 1854 book {\em The Laws of Thought\/} the mathematical analysis of Aristotelian logic was relegated to Chapter XV, the last chapter before his treatment of probability theory. This chapter is Boole's tour de force to show that he had a uniform method to obtain all valid syllogisms in his version of Aristotelian logic, namely he applied {\em reduction}, {\em elimination} and {\em solution} in that order to equational expressions for the premises. The premises of a syllogism were expressed as a pair of equations in 7 variables, but then all algebraic steps between this and the final expressions for $x$, $vx$ and $1-x$ were omitted. The somewhat tedious details of those missing steps are given in this note. It is assumed that the reader is familiar with Boole's reduction, elimination and solution theorems.