IDOL, in philosophy, means a prejudice of some kind which is a hindrance to objective, impartial or free thought. The term was first used in this sense by Giordano Bruno and adopted from him by Francis Bacon, who is chiefly responsible for the vogue which it has. Bacon distinguished four kinds of idols, namely: (I) idols of the tribe, prejudices more or less common to the whole human race; (2) idols of the cave, prejudices peculiar to individuals; (3) idols of the market place, prejudices encouraged by one's social group and mother tongue; (4) idols of the theatre, or prejudices or false notions taught and encouraged by various schools of thought.
See F. Bacon, Novum Organum.