In a specific sense, one who remains in a state of doubt, declaring all positive truth, religiousor philosophical, to be unattainable to man. This type of skeptic can scarcely be found in Judaism. However bold the Jewish philosophers of the Middle Ages were in their research or critical in their analytic methods, they never so distrusted human reason as to deny it the power, as the Greek skeptics did, to arrive at any positive knowledge or truth. Nor did the Jewish mystics attempt, as did Christian theologians, to build up a system of faith upon skepticism—that is, upon the assumption that reason is incapable of grasping any truth. Seer and sage alike appealed to reason to substantiate and verify the postulates of faith (Isa. xl. 26; Job xii. 7). The passage "The Lord is a God of knowledge" (I Sam. ii. 3) is interpreted by the Rabbis by the remark, "Great is knowledge which leads from God to God" (Ber. 33a).
Inasmuch, however, as doubt is a necessary transition from a lower stage of faith or of knowledge to a higher one, skeptics, in the sense of men wrestling with doubt, have found a certain recognition and a place of honor in Biblical literature. In a work by E. J. Dillon, entitled "The Skeptics of the Old Testament" (London, 1895), it has been well pointed out that the authors of the Book of Job, of Ecclesiastes, and of the Words of Agur, the Son of Jakeh (Prov. xxx.), were skeptics, but the original compositions were so interpolated and remodeled as to make the skeptical points no longer noticeable. All three contain bold arraignments of divine justice and providence. As to the author of Ecclesiastes compare E. H. Plumptre's edition (in "Cambridge Bible for Schools"): "He was almost driven back upon the formula of the skepticism of Pyrrho, 'Who knows?'" (p. 49). Heinrich Heine called the book "Das Hohelied der Skepsis" (see, further, Paul Haupt's "Koheleth oder Weltschmerz in der Bibel," 1905). Friedrich Delitzsch, in "Das Buch Hiob" (p. 17), calls Ecclesiastes "Das Hohelied des Pessimismus," but he might as well have called it "the Song of Skepticism."
Jewish skepticism was always chiefly concerned with the moral government of the world. The great problem of life, with "its righteous ones suffering wo, and its wicked ones enjoying good fortune," which puzzled the mind of Jeremiah (Jer. xii. 1), and Moses also, according to the Rabbis (Ber. 7a), and which finds striking expression in the Psalms (Ps. lxxiii.), created skeptics in Talmudic as well as in earlier times. According to Ḳid. 29b and Yer. Ḥag. ii. 77b, Elisha ben Abuyah became a skeptic as a consequence of seeing a person meet with a fatal accident at the very moment when he was fulfilling the two divine commandments for the observance of which Scripture holds out the promise of a long life (Deut. v. 16, xxii. 7).
The rationalistic era of Mohammedanism produced skeptics among the Jews of the time of Saadia, such as was Ḥiwi al-Balkhi, whose criticism tended to undermine the belief in revelation. The "Emunot we-De'ot" was written by Saadia, as he says in the preface, because of the many doubters who were to be convinced of the truth; and Maimonides, in the introduction to his "Moreh," states that he wrote that work as a guide for those perplexed by doubt. With all these Jewish thinkers doubt is not a sin, but an error that may reveal the pathway to the higher philosophical truth.
A remarkable type of skeptic was produced by the sixteenth century in Uriel Acosta, who, amidst a life of restless searching after truth, denied the immortality of the soul and the divine revelation. His excommunication by the Amsterdam authorities was inspired by fear of the Christian Church rather than by traditional practise. Another such was Leon of Modena, who, complaining that "the thinker is tortured by doubt, whereas the blind believer enjoys peace of mind, and bliss in the world to come" (see Ari Nohem, quoted by Grätz, "Gesch." 3d ed., x. 130), arrived through skepticism at a liberal interpretation of traditional Judaism (see S. Stern, "Der Kampf des Rabbiners Gegen den Talmud im xviii. Jahrhundert," 1902). See Agnosticism.