A Greek philosopher, born at Cyrene; his whole philosophy a polemic against the dogmatism of the Stoics, on the alleged ground of the absence of any criterion of certainty in matters of either science or morality; conceded that truth and virtue were admirable qualities, but he denied the reality of them; sent once on an embassy to Rome, he propounded this doctrine in the ears of the Conscript Fathers, upon which Cato moved he should be expelled from the senate-house and sent back to Athens, where he came from (213-129 B.C.).