Abstract

In his Autobiography John Stuart Mill said that his motivation in writing A System of Logic was to meet his opponents, those who held “the German or a priori view” of human knowledge, on their own terms. “The notion that truths external to the mind may be known by intuition or consciousness, independently of observation and experience,” he continued, “is … in these times, the great intellectual support of false doctrines and bad institutions…. There never was such an instrument devised for consecrating all deep seated prejudices.” To counteract “the German or a priori view” Mill argued that knowledge of mathematics and physical science is derived from observation and experience and that it presupposes no a priori or non-natural principles. It is comprised simply of truths known by direct experience and of truths inferred from them. Since mathematical and scientific knowledge is largely a body of inferred truths, A System of Logic is a study of the way in which truths are inferred. To quote Mill’s celebrated definition, logic is “the science of the operations of the understanding which are subservient to the estimation of evidence; both the process itself of advancing from known truths to unknown, and all other intellectual operations in so far as auxiliary to this.”