PURE LOGIC, or the Logic of Quality Apart from Quantity

In 1864 laid the foundations of his system of symbolical reasoning in a small treatise entitled "Pure Logic, or the Logic of Quality." This work did not attract at the time the attention it deserved. Although avowedly based upon the previous labors of Boole, it criticizes freely his mathematical method of handling logic, formulates a general principle of reasoning which was afterwards called by the author 'Substitution of Similars,' and works out in some detail the remarkable and comprehensive doctrine of indirect inference which is the distinctive peculiarity of the new logical calculus.