Carneades left no writings, and all that is known of his lectures is derived from his intimate friend and pupil, Clitomachus; but so true was he to his own principles of withholding assent, that Clitomachus confesses he never could ascertain what his master really thought on any subject. In ethics, which more particularly were the subject of his long and laborious study, he seems to have denied the conformity of the moral ideas with nature. This he particularly insisted on in the second oration on Justice, in which he manifestly wished to convey his own notions on the subject; and he there maintains that ideas of justice are not derived from nature, but that they are purely artificial for purposes of expediency.
