The art of reasoning, and one of the Seven Liberal Arts and Sciences, whose uses are incuLcated in the Second Degree. The power of right reasoning, which distinguishes the man of sane mind from the madman and the idiot, is deemed essential to the Freemason, that he may comprehend both his rights and his duties. And hence the unfortunate beings just named, who are without this necessary mental quality, are denied admission into the Order. The Old Charges define logic to be the art "that teacheth to discern truth from falsehood."
- Source: Mackey's Encyclopedia of Freemasonry