For a man of the modern time, perhaps the most interesting expression that ever fell from Roger Bacon’s lips is his famous proclamation of the reasons why men do not obtain genuine knowledge more rapidly than would seem ought to be the case, from the care and time and amount of work which they have devoted to its cultivation. This expression occurs in Bacon’s Opus Tertium, which, it may be recalled, the Franciscan friar wrote at the command of Pope Clement, because the Pope had heard many interesting accounts of all that the great thirteenth century teacher and experimenter was doing at the University of Oxford, and wished to learn for himself the details of his work. Friar Bacon starts out with the principle that there are four grounds of human ignorance.
“These are: first, trust in adequate authority; second, that force of custom which leads men to accept too unquestioningly what has been accepted before their time; third, the placing of confidence in the opinion of the inexperienced; and fourth, the hiding of one’s own ignorance with the parade of superficial knowledge.” These reasons contain the very essence of the experimental method, and continue to be as important in the twentieth century as they were in the thirteenth. They could only have emanated from an eminently practical mind, accustomed to test by observation and by careful searching of authorities every proposition that came to him.
James J. Walsh, The Popes and Science (1908)