520 



fULLACIES. 



vegetable juice, in order to discover 

 in it some traces of an acid or alkaline 

 ingredient, which might confer upon 

 it medicinal activity. The fatal errors 

 into which such an hypothesis was 

 liable to betray the practitioner re- 

 ceived an awful illustration in the 

 history of the memorable fever that 

 raged at Ley den in the year 1699, 

 and which consigned two-thirds of 

 the population of that city to an un- 

 timely grave ; an event which in a 

 great measure depended upon the 

 Professor Sylvius de la Boe, M'ho 

 having just embraced the chemical 

 doctrines of Van Helniont, assigned 

 the origin of the distemper to a pre- 

 vailing acid, and declared that its 

 cure could alone [only] be effected by 

 the copious administration of absor- 

 bent and testaceous medicines." * 



These aberrations in medical theory 

 have their exact parallels in politics. 

 All the doctrines which ascribe ab- 

 solute goodness to particular forms 

 of government, particular social ar- 

 rangements, and even to particular 

 modes of education, without reference 

 to the state of civilisation and the 

 various distinguishing characters of 

 the society for which they are in- 

 tended, are open to the same objec- 

 tion — that of assuming one class of 

 influencing circumstances to be the 

 paramount rulers of phenomena which 

 depend in an equal or greater degree 

 on many others. But on these con- 

 siderations it is the less necessary 

 that we should now dwell, as they 

 will occupy our attention more largely 

 in the concluding Book. 



§ 6. The last of the modes of 

 erroneous generalisation to which I 

 shall advert is that to which we may 

 give the name of False Analogies. 

 This Fallacy stands distinguished 

 from those already treated of by the 

 peculiarity that it does not even 

 simulate a complete and conclusive 

 induction, but consists in the mis- 

 application of an argument which is 



* Pharmacologia, p. 39-40- 



at best only admissible as an incon- 

 clusive presumption where real proof 

 is unattainable. 



An argument from analogy is an 

 inference that what is true in a cer- 

 tain case is true in a case known to 

 be somewhat similar, but not known 

 to be exactly parallel, that is, to be 

 similar in all the material circum- 

 stances. An object has the property 

 B ; another object is not known to 

 have that property, but resembles 

 the first in a property A, not known 

 to be connected with B ; and the 

 conclusion to which the analogy 

 points is that this object has the 

 property B also. As, for example, 

 that the planets are inhabited because 

 the earth is so. The planets resem- 

 ble the earth in describing elliptical 

 orbits round the sun, in being at- 

 tracted by it and by one another, in 

 being nearly spherical, revolving on 

 their axes, &c., and, as we have now 

 reason to believe from the revelations 

 of the spectroscope, are composed, iii 

 great part at least, of similar mate- 

 rials ; but it is not known that any of 

 these properties, or all of them to- 

 gether, are the conditions on which 

 the possession of inhabitants is de- 

 pendent, or are marks of those condi- 

 tions. Nevertheless, so long as we 

 do not know what the conditions are, 

 they viay be connected by some law 

 of nature with those common proper- 

 ties ; and to the extent of that possi- 

 bility the planets are more likely to 

 be inhabited than if they did not re- 

 semble the earth at all. This non- 

 assignable and generally small in- 

 crease of probability beyond what 

 would otherwise exi t is all the evi- 

 dence which a conclusion can derive 

 from analogy. For if we have the 

 slightest reason to suppose any real 

 connection between the two proper- 

 ties A and B, the argument is no 

 longer one of analogy. If it had 

 been ascertained (I purposely put an 

 absurd supposition) that there was a 

 connection by causation between the 

 fact of revolving on an axis and 

 the existence of animated beings, OJ? 



