FALLACIES OF OBSERVATION. 483 



minute in amount, and generally so unimpoilant a portion of the state 

 of facts which we wish to ascertain or to communicate, it would be 

 absurd to say that either in Our observations, or in conveying their 

 result to others, we ought not to mingle inference with fact ; all thut 

 can be said is, that when wo do so we ought to be aware of what we 

 aie doing, and to know what part of the assertion rests upon conscious- 

 ness, and is therefore indisputable, what part upon inference, and is 

 therefore questionable. 



One of the most celebrated examj)lcs of an univei-sal error produced 

 by mistaking an inference tor the direct e%-idence of the senses, was 

 the resistance made, on the ground of conunon sense, to the Copernican 

 system. People fancied they at/ /r the sun rise and set, the stars revolve 

 m circles round the pole. We now know that they saw no such thing: 

 what they really saw were a set of appearances, equally reconcila- 

 ble with the theory they held and with a totally diHerent one. It 

 seems strange that such an instance as this, of the testimony of the 

 senses pleaded with the most entire conviction in favor of something 

 which was a mere inference of the judgment, and, as it turned out, 

 a false inference, should not have (opened the eyes of the bigots 

 of common sense, and inspired them with a more modest distrust 

 of the competency of mere ignorance to judge the conclusions of 

 science. 



In proportion to any person's deficiency of knowledge and mental 

 cultivation, is generally his inability to discriminate between his infer- 

 ences and the perceptions on which they were grounded. INIany a 

 marvelous tale, many a scandalous anecdote, owes its origin to this 

 incapacity. The narrator relates, not what he saw or heard, but the 

 impression which he derived from what he saw or heard, and of which 

 perhaps the greater part consisted of inference, though the whole is 

 related not as inference, but as matter-of-fact. The difficulty of in- 

 ducing witnesses to restrain within any moderate limits the intermix- 

 ture of their inferences with the naiTative of their perceptions, is well 

 known to experienced cross-examiners ; and still more is this the case 

 when ignorant persons attempt to describe any natural phenomenon. 

 "The simplest narrative," says Dugald Sttnvart,* "of the most illiterate 

 obscner involves more or less of hypothesis ; nay, in general, it will 

 be found that, in proportion to his ignmance, the gieater is the number 

 of conjectural principles involved in his statements. A village pothe- 

 cary (and, if possible, in a still greater degree, an experienced nurse) 

 is seldom able to describe the plainest case, without employing a phra- 

 seology of which every word is a theory ; whereas a simph; and gen- 

 uine specification of the phenomena which mark a particular disease, 

 a specification unsophisticated l>y fancy, or by preconceivtul opinions, 

 may be regarded as unequivocal evidence of a mind trained by long 

 and successful study to the most difficult of all arts, that of the fuilhfui 

 interpretation of nature.''t 



* Elements of the Philosophy of the Mind, vol. ii., ch. 4, sect. 5. 



tThe following anecdote, related by Dr. Paris (Pharmacologia, pp. 7G-7), is an amusing 

 instance of an inference mistaken for a direct perception. "Shortly after Sir Humphry 

 Davy had succeeded in decomposing the fi.xcd alkalies, a portion of potassium" (a sub- 

 stance so light as to swim upon water) " was placed in the hand of one of our most dis- 

 tinguished chemists, with a query as to its nature. The philosopher observing its aspect 

 and splendor did not hesitate in pronouncing it to be metallic, and uniting at once the idea 

 of weight with that of metal, the evidence of his senses was even insulficient to dissever 



