Free-Thinkers, those who, abandoning the religious truths and moral dictates of the Christian Revelation, and accepting no dogmatic teaching on the ground of authority, base their beliefs on the unfettered findings of reason alone. Free-thought, of which they make profession, is an exaggerated form, though a quite logical development, of the doctrine of private judgment in religious matters. The free-thinker holds such principles, whether of truth or of action, as he is persuaded that he can prove; and he gives assent to no others. He is a rationalist. But since the persuasion of having proved (or of being able to prove) even the doctrines of natural religion by reason alone varies indefinitely with the individual, it is difficult, save on the most general lines, to class free-thinkers together. This difficulty is apparent in the case of the Deists, to whom the appellation was characteristically applied in the latter end of the seventeenth century. They all agree, however, in refusing to accept the doctrines of an authoritative Christianity; and it is on this negative ground that their position is most clearly defined.
Although the words “Free-thinker” and “Free-thought” first appeared in connection with the English Deists [Collins, “Discourse of Freethinking occasioned by the Rise and Growth of a Sect called Freethinkers” (1713), gives the deistical tendency this name], “the phenomenon of free-thought has existed, in specific form, long before it could express itself in propagandist writings, or find any generic name save those of Atheism or Infidelity” (Robertson). Taken in the broad sense in which Robertson here uses it, the term would seem to include the reactionary movement against any traditional form of doctrine to which men were expected to assent. In this sense it is possible to speak of free-thinkers of Greece or Rome, or, indeed, of any considerable body that can impress its teaching upon the multitudes. There were undoubtedly, to a certain extent at any rate, in classical times those who either publicly scoffed at the authoritative myths of their country’s religion or philosophically explained their meaning away. So—but this in a truer sense—in the Middle Ages there were to be found rationalists, or free-thinkers, among the philosophers of the schools. The Fathers of the Church had met paganism with its own weapons and argued against its falsehoods with the help of the natural reason. The early heretics were free-thinkers in their rejection of the regulating authority of the Church upon points connected with their heresies, which they elaborated frequently upon rationalistic lines; and the pantheists and others of the schools criticized and syllogized revelation away in true free-thought style. Both were in consequence condemned; but the spirit of excess in criticism and the reliance on the sufficiency of human reason are as typical of the free-thought of medieval times as of that of the twentieth century.
From the Deists onwards, free-thought has undoubtedly gained ground among the masses. Originally the intellectual excess of the learned and the student, and rarely leaving the study in a form in which it could be expected to be at all popular, it began with Annet and Chubb (see Deism) to become vulgarized and to penetrate the lower strata of society. Its open professors have apparently always been less numerous than its adherents. Some stop short in a negative position, claiming no more than an autonomy for the science or philosophy they represent. Others carry on a bitter and unscrupulous warfare against religion. It is apparent in the various branches of science and criticism, as well as in philosophy; and though it generally pretends to a scientific plan it makes use of a priori methods more than a posteriori ones. One of its most dangerous forms, which generally ends in pure religious scepticism, can be traced to the Kantian distinction between the noumenal and the phenomenal. But its main positive positions are the denial of prophecy, miracle and inspiration, its rejection of all external revelation (including obviously ecclesiastical authority), and its assertion of the right of free speculation in all rational matters. On this latter frequently follows the negation of, or suspension of judgment with regard to, the existence of God (atheism and agnosticism), the denial of the immortality of the soul or of its truth being susceptible of proof, and the rejection of the freedom of the will. Among the principal free-thinkers may be mentioned Voltaire, Thomas Paine (The Rights of Man), Renan, Ingersoll, Strauss (Leben Jesu), Haeckel, Clough, and Holyoake.