CARNEADES (214–129 B.C.), Greek philosopher, founder of the Third or New Academy, was born at Cyrene. Little is known of his life. He learned dialectics under Diogenes the Stoic, and under Hegesinus, the third leader, of the Academy in descent from Arcesilaus. The chief objects of his study, however, were the works of Chrysippus, opposition to whose views is the mainspring of his philosophy. “If Chrysippus had not been,” he is reported to have said, “I had not been either.” In 155, together with Diogenes the Stoic and Critolaus the Peripatetic, he was sent on an embassy to Rome to justify certain depredations committed by the Athenians in the territory of Oropus. On this occasion he delivered two speeches on successive days, one in favour of justice, the other against it. His powerful reasoning excited among the Roman youth an enthusiasm for philosophical speculations, and the elder Cato insisted on Carneades and his companions being dismissed from the city.
Carneades, practically a 5th-century sophist, is the most important of the ancient sceptics. Negatively, his philosophy is a polemic against the Stoic theory of knowledge in all its aspects. All our sensations are relative, and acquaint us, not with things as they are, but only with the impressions that things produce upon us. Experience, he says, clearly shows that there is no true impression. There is no notion that may not deceive us; it is impossible to distinguish between false and true impressions; therefore the Stoic φαντασἰα καταληπτική (see Stoics) must be given up. There is no criterion of truth. Carneades also assailed Stoic theology and physics. In answer to the doctrine of final cause, of design in nature, he points to those things which cause destruction and danger to man, to the evil committed by men endowed with reason, to the miserable condition of humanity, and to the misfortunes that assail the good man. There is, he concludes, no evidence for the doctrine of a divine superintending providence. Even if there were orderly connexion of parts in the universe, this may have resulted quite naturally. No proof can be advanced to show that this world is anything but the product of natural forces. Carneades further attacked the very idea of God. He points out the contradiction between the attributes of infinity and individuality. Like Aristotle, he insists that virtue, being relative, cannot be ascribed to God. Not even intelligence can be an attribute of the divine Being. Nor can he be conceived of as corporeal or incorporeal. If corporeal, he must be simple or compound; if a simple and elementary substance, he is incapable of life and thought; if compound, he contains in himself the elements of dissolution. If incorporeal, he can neither act nor feel. In fact, nothing whatever can be asserted with certainty in regard to God. The general line of argument followed by Carneades anticipates much in modern thought.
The positive side of his teaching resembles in all essentials that of Arcesilaus (q.v.). Knowledge being impossible, a wise man should practise ἐποχή (suspension of judgment). He will not even be sure that he can be sure of nothing. Ideas or notions are never true, but only probable; nevertheless, there are degrees of probability, and hence degrees of belief, leading to action. According to Carneades, an impression may be probable in itself; probable and uncontradicted (ἀπερίσπαστος, lit. “not pulled aside,” not distracted by synchronous sensations, but shown to be in harmony with them) when compared with others; probable, uncontradicted, and thoroughly investigated and confirmed. In the first degree there is a strong persuasion of the propriety of the impression made; the second and third degrees are produced by comparisons of the impression with others associated with it, and an analysis of itself. His views on the summum bonum are not clearly known even to his disciple and successor Clitomachus. He seems to have held that virtue consisted in the direction of activity towards the satisfaction of the natural impulses. Carneades left no written works; his opinions seem to have been systematized by Clitomachus.
See A. Geffers, De Arcesilae Successoribus (1845); C. Gouraud, De Carneadis Vita et Placitis (1848); V. Brochard, Les Sceptiques grecs (1887); C. Martha, “Le Philosophe Carneade a Rome,” in Revue des deux mondes, xxix. (1878), and the histories of philosophy; also Academy, Greek.