ERROR AMD FALLACIES 331 



they have seen ghosts when they have really seen tombstones 

 or stray donkeys. It requires some reflection to realize what a 

 vast amount of inference is inseparably bound up in sense per 

 ception. The success of conjuring, ventriloquism, etc., is based 

 on our partial incapacity to separate, from what we actually see 

 or hear, our own misleading inferences, and our habitual associa 

 tions of ideas. In all such cases of error, it is in the interpretation 

 the mistake is committed, not in the perception itself: the sense- 

 impression is always what it ought to be in the circumstances. 

 So it is when, looking from a train which is stationary at another 

 which is passing close by, we imagine that the latter is at rest 

 and our own train in motion. So, too, we imagine that we 

 see the sun moving around the earth, and the stars revolving 

 around the pole, when it is really the diurnal revolution of the 

 earth on its axis that causes those appearances. Our only safe 

 guard against mal-observation is a lively advertence to its ever- 

 present dangers, together with the fullest knowledge we can 

 acquire on the subject-matter under investigation. 



() FALSE ANALOGY. We have seen that analogy is a fertile 

 source of scientific hypothesis (234). An analogy or resemblance 

 which is only apparent, not real, is called a false analogy. The 

 points of similarity are not due to the operation of some common 

 cause. Hence, an hypothesis based on such an analogy will be 

 misleading, and must be abandoned ; and this often happens in 

 scientific research. Or, again, the observed analogy may indeed 

 be real, but may have been assumed by the inquirer to be more, 

 or less, extensive than it really is ; he may misinterpret it and 

 extend its scope unduly in one direction, or fail to apprehend 

 its real application in another direction. An analogy whose 

 scope and weight are thus wrongly estimated, may be called an 

 imperfect analogy ; the hypothesis based upon it will need to 

 be remoulded before it can be verified, and so transformed into 

 a law. This, too, frequently occurs in science: indeed it may 

 be regarded as the usual procedure in inductive research. Non- 

 observation of operative influences is the most frequent cause of 

 imperfection in our analogies. 



It is a common mistake to miss the point of an analogy, that 

 is, to misinterpret its real significance, to base upon it an infer 

 ence, conclusion, or hypothesis, other than that to which it really 

 points. If the just man shows skill in regard to the possession 

 of property, it does not follow (as the Platonic Socrates humor- 



