To avoid the various foolish opinions to which mankind are prone, nosuperhuman genius is required. _（1）. A few simple rules will keep you, notfrom all error ,but from silly error_. _（2）. If the matter is one that can be settled by observation, make theobservation yourself_. Aristotle could have avoided the mistake of thinkingthat women have fewer teeth than men, by the simple device of asking Mrs.Aristotle to keep her mouth open while he counted. He did not do so because he thought he knew. _（3）. Thinking that you know when in fact you don'tis afatal mistake, to which we are all prone_. I believe myself that hedgehogs eatblack beetles , because I have been told that they do ;but if I were writing abook on the habits of hedgehogs, I should not commit myself until I had seenone enjoying this unappetizing diet . Aristotle ,however ,was less cautious .Ancient and medieval authors knew all about unicorns and salamanders ;not oneof them thought it necessary to avoid dogmatic statements about them becausehe had never seen one of them. Many matters, however ,are less easily brought to the test of experience._66\. If, like most of mankind, you have passionate convictions on many suchmatters, there are ways in

which you can make yourself aware of your ownbias_. If an opinion contrary to your own makes you angry, that is a sign thatyou are subconsciously aware of having no good reason for thinking as you do._67\. If someone maintains that two and two are five, or that Iceland is onthe equator, you feel pity rather than anger_. (From How to Avoid the Foolish Opinions)