ERROR AND FALLACIES 333 



notions. In this dissemination of error, the fallacy of illicit 

 generalization plays a large part. The wildest guesses, the 

 merest speculations of the scientist, are proclaimed as established 

 truths of science ; and verified laws are extended beyond their 

 rightful domain. This fallacious procedure has special reference 

 to the formation and verification of scientific hypotheses^ and to 

 the establishment of scientific truths or laws. It may assume a 

 variety of forms. 



In the process of verifying an hypothesis, and so setting it up, 

 and yielding our assent to it, as a general principle or law, we 

 sometimes succumb to the temptation of ignoring extreme cases, 

 which, if taken into account, would necessitate a modification and 

 restatement of our general conclusion. &quot; The application of the 

 extreme case is very often the only test by which an ambiguous 

 assumption [or generalization] can be dealt with. . . . Where any 

 thing is asserted which is true with exceptions, there is often great 

 difficulty in forcing the assertor to attempt to lay down a canon 

 by which to distinguish the rule from the exception? Yet everything 

 depends upon this, &quot; for the question will always be whether the 

 example belongs to the rule or the exception &quot;. But &quot; when 

 one case is brought forward which is certainly an exception, the 

 assertor will, in nine cases out of ten, refuse to see why it is 

 brought forward. He will treat it as a fallacious argument 

 against the rule, instead of admitting that it is a good reason why he 

 should define the method of distinguishing the exceptions&quot; * Such 

 an attitude is, of course, in flagrant antagonism to the method 

 by which hypotheses can be accurately moulded into scientific 

 laws (234, 240). A scientific law should be so stated as to ad 

 mit of no &quot;exceptions&quot; other than those for which the state 

 ment of it makes express provision : &quot; A rule may have exceptions, 

 it is said ; but this is hardly a correct statement. A rule with 

 exceptions is no rule, unless the exceptions be definite and deter- 

 minable : in which case the exceptions are exclusions by another 

 rule.&quot; * 



The fallacy to which empirical generalizations (247) are 

 most exposed, is that of wrongly interpreting their scope and im 

 port : of mistaking them for established universal laws, and so 

 extending them to cases which they do not, or at least may not, 



1 DE MORQAN, Formal Logic, pp. 270-1 ; apud WELTON, op. cit., p. 271 (italics 

 ours). 



8 ibid., p. 272. 



