To avoid the various foolish opinions to which mankind is liable, no superhuman genius is required. A few rules will keep you, not from all errors, but from silly errors. 　　If the matter is one that can be settled by observation, make the observation yourself. Aristotle could have avoided the mistake of thinking that women have fewer teeth than men, by the device of asking Mrs. Aristotle to keep her mouth open while he counted. He did not do so because he thought he knew. Thinking that you know when in fact you don’’t is a fatal mistake, to which we are all liable. 　　Many matters, however, are less easily brought to the test of experience. If, like most of mankind, you have strong convictions on many such matters, there are ways in which you can make yourself aware of your own prejudice. If an opinion contrary to your own makes you angry, that is a sign that you subconsciously are aware of having no good reason for thinking as you do. If someone maintains that two and two are five, or that Iceland is on the equator, you feel pity rather than anger, unless you know so little of arithmetic or geography that his opinion shakes your own contrary conviction. The most savage controversies are those about matters as to which there is no good evidence either way. So whenever you find yourself getting angry about a difference of opinion, be on your guard; you will probably find, on examination, that your belief is going beyond what the evidence justifies. 　　For those who have enough psychological imagination, it is a good plan to imagine an argument with a person having a different opinion. This has one advantage, and only one, ascompared with actual conversation with opponents; this one advantage is that the method is not subject to the same limitations of time and space. Mahatma Gandhi (圣雄甘地) considered it unfortunate to have railways and steamboats and machinery; he would have liked to undo the whole of the industrial revolution. You may never have an opportunity of actually meeting anyone who holds this opinion, because in Western countries most people take the advantage of modern technology for granted. But if you want to make sure that you are right in agreeing with the prevailing opinion, you will find it a good plan to test the arguments that occur to you by considering what Gandhi might have said in refutation of them. I have sometimes been led actually to change my mind as a result of this kind of imaginary dialogue. Furthermore, I have frequently found myself growing more agreeable through realizing the possible reasonableness of a hypothetical opponent. According to the text, it is true that