The idola fori, which arise from the use of language in public intercourse, depend upon the confusion of words, which are mere symbols with a conventional value and which are based on the carelessly constructed concepts of the vulgar, with things themselves.

Et per istum modum fratres maximam multitudinem baptizant, qui citò recidiuant ad idola pecorum: qui fratres continuò quasi stent cum illis, et illos informent.

The idola specus are individual prepossessions which interfere with the apprehension of the true state of affairs, such as the excessive tendency of thought toward the resemblances or the differences of things, or the investigator's habit of transferring ideas current in his own department to subjects of a different kind.

The most dangerous are the idola theatri, which consist in the tendency to put more trust in authority and tradition than in independent reflection, to adopt current ideas simply because they find general acceptance.