Roger Bacon...on the causes of error

There ar four very significant stumbling blocks in the way of grasping the truth which hinder every man, however learned, and scarcely allow anyone to win a clear title to wisdom, namely, the example of weak and unworthy authority, long-standing custom, the feeling of the ignorant crowd, and the hiding of our own ignorance while making a display of our apparent knowledge. Every man is involved in these things, every rank is affected. For every person, whatever walk of life, both in application to study and in all forms of occupation, arrives at the same conclusion by the three worst arguments, namely, this is the pattern set by our elders, this is the custom, this is the popular belief: therefor it should be held.

- Opus Majus, 1.1 13th Cent.