The four idols distinguished by Francis Bacon are the idols of the tribe, den, market, and theatre. Idols in this sense are eidola, the transient, and therefore to Bacon erroneous, images of things.

1. (i) Idols of the tribe are general tendencies to be deceived, inherent in our nature as human beings. They include uncritical reliance on sense perception, and tendencies to overgeneralize or jump to conclusions and ignore countervailing evidence against our views.

2. (ii) Idols of the den are distortions arising from our particular perspectives (the metaphor is that of Plato’s myth of the cave); the corrective is to remember that whatever our mind ‘seizes and dwells upon with peculiar satisfaction is to be held in suspicion’.

3. (iii) Idols of the market-place are errors that come in the course of communication with others: misunderstandings arising through abuses of words.

4. (iv) Idols of the theatre are the errors introduced by theories: the abstract schemata of Aristotelianism, and the introduction of theological notions into science.

Bacon here compared philosophical and religious systems to theatrical, and therefore fantastical, representations of the world.