Carneades (c. 214 - 129 B.C.E.) was one of the most prominent Academic skeptics. Head of the Academy from 167 to 137 B.C.E., he not only argued against the dogmatic positions of other philosophers; he developed arguments in favor of views that had never been considered before, in order to demonstrate that no conclusion can be held to be absolutely true. His interest was mainly in ethics and epistemology, and he excelled in oratory and dialectic. He made several significant philosophical contributions, including arguments against determinism, and discussions of the truth-value of statements about the future and human freedom. His system for classifying the ethical values of various thought processes became a standard philosophical framework. He developed a skeptic criterion for judging the accuracy of a sense impression by evaluating its relative plausibility (to pithanon). It is unclear whether Carneades himself completely accepted this criterion as valid and useful.
Ancient writers referred to Carneades as the founder of the “third” or “New” Academy, following the second or Middle Academy of Arcesilaus and the first or Old Academy of Plato and his successors. Carneades modified skepticism to allow for the validity of well-founded opinions, which opened skeptical debate to other topics besides epistemology, such as theology, metaphysics, and natural philosophy. Later skeptics devoted themselves to understanding and interpreting the thought of Carneades.
Carneades was born in Cyrene (a Greek city in North Africa) c. 214 B.C.E. and came to Athens, where he studied logic under the Stoic, Diogenes of Babylon, the fifth head of the Stoa and a student of Chrysippus. Diogenes Laertius reports, in Lives of Eminent Philosphers, that, "he read all the books of the Stoics with great care, and especially those of Chrysippus; and then he wrote replies to them, but did it at the same time with such modesty that he used to say, 'If Chrysippus had not lived, I should never have existed.'"
In 137 B.C.E., Carneades became head of the Academy, succeeding Arcesilaus, Lacydes (c. 243 B.C.E.), Evander, and Hegesinus. He was a gifted orator. Diogenes Laertius describes him as a “man of great industry,” and great voice, “a very vehement speaker, and one difficult to contend with in the investigation of a point.” He also says that Carneades was so devoted to philosophical discussion that he did not find time to cut his hair and nails, and that he was such an eminent philosopher that other orators left their schools to come and listen to his lectures.
Carneades was sent to Rome in 155 B.C.E., together with Diogenes and Critolaus, head of the Perpipatos, to present an Athenian petition before the senate. According to Plutarch, in Life of Cato the Elder, studious Roman youths came immediately to hear the philosophers speak, and the gracefulness of Carneades’ oratory attracted a large audience. On two successive days, Carneades argued for and against justice, outraging the Roman elders. Cato, who did not like philosophy, was annoyed and concerned that Roman young men would turn their attention from warfare to philosophy. He ordered the senate to respond to the Athenian petition quickly, so that the philosophers would go back to Greece.
Carneades was renowned for his skill in arguing against the positions of other philosophers, particularly the Stoics. He followed the dialectical tradition of Socrates and Arcesilaus, which was, according to Cicero, to conceal his private opinions, use a series of questions to reveal the weaknesses of his opponents’ position, and in doing so, to search for the most probable solution. Later writers consider Carneades the founder of the third or New Academy, signaling a change in philosophical approach from the second or Middle Academy of Arcesilaus, and the first or Old Academy of Plato. Carneades’ skepticism appeared to be less extreme than the position of his predecessors, admitting the usefulness of well-founded opinions, and thus allowing him to diverge from epistemology to other topics, such as ethics, natural philosophy, and theology.
Carneades died at the age of eighty-five in 129 B.C.E. Legend says that an eclipse of the moon took place at the time of his death.
Carneades left no written works except for a few letters, which were lost. His thought was transmitted to his students in his lectures and discussions, and was preserved by his successor as head of the Academy, Clitomachus, whose works were interpreted in detail by later writers, including Cicero and Sextus Empiricus.
Carneades devoted much of his effort to exposing the weaknesses of Stoic arguments, but he went further, setting forth arguments of his own in favor of views that sometimes had never been defended before, not in order to establish their truth, but simply to demonstrate that no argument could be assumed to be true. He also challenged the precepts of other schools of thought, including the Epicureans. Much of the work of the later Skeptics involved interpretation and commentary on the ideas of Carneades.
The Stoics used cognitive impressions as the basis by which truth could be perceived. Carneades argued that a cognitive impression could be in error because there were instances where entirely different objects or circumstances, such as identical twins or a mirror image, could produce identical cognitive impressions. In such cases, the only way to avoid error would be to suspend judgment. The Stoic counter-argument was that, without cognitive impressions, human beings would have no basis for making inquiries or acting. Carneades replied that such a basis could be found in “probable impressions.” Certain sense impressions would appear to be more convincing than others. If a sense impression is sufficiently convincing, and if it correlates with other relevant impressions, it can be used as a basis for action. There may be occasions when the sense impression is not accurate, but these do not occur often in daily life. When an important decision is to be made, particularly one relating to happiness, further inquiries can be made to verify the validity of the sense impression. It is unclear whether Carneades himself endorsed the criterion of “probability,” (to pithanon) or whether he was merely setting forth a philosophical proposal for consideration. Clitomachus, his successor and closest associate, did not know what Carneades thought, but he testified that Carneades worked diligently to “cast assent …, like a wild and savage beast, that is mere opinion and thoughtlessness" out of the minds of his listeners.
Carneades set out to classify not only the existing ethical theories of his time, but any others that might be possible. He argued that in order to conduct life successfully, human beings must have an object, the greatest good, and the accomplishment of it must be something towards which man had a natural impulse. He identified three possible objects of goodness: Pleasure, freedom from pain, and natural advantages such as health and strength. Virtue was action with the purpose of attaining one, or more of these objects. He proposed six simple views of the goal of life, the achievement of each of the three objects and the virtue of acting towards the attainment of each object; and three views which combined striving to achieve the object with the accomplishment of the object itself. This classification influenced the way in which later philosophers examined ethical theories. The Stoic concept, that virtue is the only good, corresponded with the sixth simple goal of always acting in order to achieve natural advantages.
Entering into the debate between the Stoics and the Epicureans on determinism and Free Will, Carneades argued that the principle of bivalence (the principle that for any statement P, either P is true or P is false) does not imply deterministic consequences. A statement could be true today and false tomorrow, if a different choice is made tomorrow. He also said that the Epicureans did not need the concept of a “random atomic swerve” to liberate human lives from causal determinism. The free movement of a person’s mind was cause enough for his actions, without any other necessity.
Carneades also challenged the Epicurean and Stoic concepts of the gods, using a logical argument that since they could not consistently define what was divine and what was not, there was a possibility that everything could be divine.
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