Scepticism (Gr. skeptomai, 'I consider') strictly denotes that condition in which the mind is before it has arrived at conclusive opinions—when it is still in the act of reflecting, examining, or pondering subjects of thought. Scepticism is therefore the opposite of dogmatism. The notion of 'disbelief' is quite a secondary meaning of the term. Among the Greeks a skeptikos, 'sceptic,' was a thoughtful, inquiring person. But inasmuch as the mass of men rush to conclusions with haste, and assert them with far more positiveness than their knowledge warrants, the discerning few of clearer vision are often brought into collision with popular beliefs—more especially in religion, the sphere in which popular beliefs are most numerous, most positive, and most inconsiderate—and are compelled, by the shock given to their reason, to 'doubt,' it may be to 'disbelieve' what is believed and affirmed by the multitude. Thus it is that in common parlance a sceptic has come to mean an infidel, and scepticism infidelity. But the field of thought in which scepticism properly so called exercised itself is not religion but philosophy. In philosophy too the word acquired a meaning different from doubt, or the negation of dogmatism; there was a distinct tendency on the part of those called sceptics to avoid coming to a conclusion one way or another. Philosophical sceptics in all ages and countries have not so much used doubt, like Descartes, as a philosophical instrument; they seem generally to have denied or at least doubted the trustworthiness of the senses as vehicles of absolute truth, and so have destroyed the very possibility of speculation. Pyrrho (q.v.) was the head of the first great school of professed sceptics; the Second Academy under Arcesilaus, and the Third under Carneades, were less thoroughly sceptical. The teaching of the Sophists (q.v.) was also sceptical in temper and tendency. In modern times David Hume represented advanced scepticism in philosophy (as well as in theology); and Kant's opposing philosophy, or a large part of it, has been made the foundation of sceptical systems. The doctrine of the Relativity of Knowledge (q.v.) taught by Hamilton and Mansel may easily be pushed to a highly sceptical extreme. Comte's positivism is in the metaphysical sphere even dogmatically sceptical; in Secularism (q.v.) there is a scepticism of indifference towards all theological and religious doctrine; while Agnosticism (q.v.) may fairly be described as combining most of the characteristic features of philosophical and theological scepticism.
See the articles referred to above; the histories of philosophy; Green's Introduction to Hume's works; Balfour's Defence of Philosophic Doubt; and Rev. J. Owen's three works on the Sceptics (1881-93).