Roger Bacon, The Opus Majus of Roger Bacon

"If in other sciences we should arrive at certainty without doubt and truth without error, it behooves us to place the foundations of knowledge in mathematics..."

"Now there are four chief obstacles in grasping truth, which hinder every man, however learned, and scarcely allow anyone to win a clear title to learning, namely, submission to faulty and unworthy authority, influence of custom, popular prejudice, and concealment of our own ignorance accompanied by an ostentatious display of our knowledge."