 Boole approached logic from a completely different perspective, namely how to cast Aristotelian logic in the garb of symbolical algebra. Using symbolical algebra was a theme with which he was well-acquainted from his work in differential equations, and from the various papers of his young friend and mentor Duncan Farquharson Gregory (1813–1844), who made attempts to cast other subjects such as geometry into the language of symbolical algebra. Since the application of symbolical algebra to differential equations had proceeded through the introduction of differential operators, it must have been natural for Boole to look for operators that applied in the area of Aristotelian logic. He readily came up with the idea of using “selection” operators, for example, a selection operator for the color red would select the red members from a class. In his 1854 book, Boole realized that it was simpler to omit selection operators and work directly with classes. (However he kept the selection operators to justify his claim that his laws of logic were not ultimately based on observations concerning the use of language, but were actually deeply rooted in the processes of the human mind.) From now on in this article, when discussing Boole’s 1847 book, the selection operators have been replaced with the simpler direct formulation using classes.