The first are Idols of the Tribe--"man's sense is falsely asserted to be the standard of things." These are "inherent in human nature."
Second are Idols of the Den--besides the errors common to all humans, each individual has his or her own den "which intercepts and corrupts the light of nature, either from his own peculiar and singular disposition, or from his education and intercourse with others, or from his reading, and the authority acquired by those whom he reverences and admires, for from the different impressions produced on the mind."
Next are Idols of the Market--these are false ideas generated by our social interactions. Bacon emphasizes the role language plays: "words still manifestly force the understanding, throw everything into confusion, and lead mankind into vain an innumerable controversies and fallacies."
Finally, there are Idols of the Theatre--these arise from "the various dogmas of peculiar systems of philosophy." Bacon wrote, "For we regard all the systems of philosophy hitherto received or imagined, as so many plays brought out and performed, creating fictitious and theatrical worlds." Wow! That sounds like someone writing in the 20th or 21st centuries.
What can rid us of these idols? "The formation of notions and axioms on the foundation of true induction is the only fitting remedy by which we can ward off and expel these idols."