there maintains that ideas of justice are not derived from nature, but that they are purely artificial for purposes of expediency. All this, however, was nothing but the special application of his general theory, that people did not possess, and never could possess, any criterion of truth. Carneades argued that, if there were a criterion, it must exist either in reason (logos), or sensation (aisthêsis), or conception (phantasia). But then reason itself depends on conception, and this again on sensation; and we have no means of judging whether our sensations are true or false, whether they correspond to the objects that produce them, or carry wrong impressions to the mind, producing false conceptions and ideas, and leading reason also into error. Therefore, sensation, conception, and reason, are alike disqualified for being the criterion of truth. But after all, people must live and act, and must have some rule of practical life; therefore, although it is impossible to pronounce anything as absolutely true, we may yet establish probabilities of various degrees. For, although we cannot say that any given conception or sensation is in itself true, yet some sensations appear to us more true than others, and we must be guided by that which seems the most true. Again, sensations are not single, but generally combined with others, which either confirm or contradict them; and the greater this combination the greater is the probability of that being true which the rest combine to confirm; and the case in which the greatest number of conceptions, each in themselves apparently most true, should combine to affirm that which also in itself appears most true, would present to Carneades the highest probability, and his nearest approach to truth. See also Academica (Cicero) Anti-realism Moral relativism Philosophical skepticism Pyrrhonism Subjectivism Notes Sources External links 210s BC births 120s BC deaths 2nd-century BC Greek people 2nd-century BC philosophers Cyrenean Greeks Academic philosophers Ancient Greeks in Rome Ancient Skeptic philosophers Hellenistic-era philosophers in Athens