ERROR AND FALLACIES 313 



vious analogy between the simple conversion of the categorical 

 &quot;A &quot; proposition in the fallacy of the accident, and the attempt to 

 argue from consequent to antecedent in the hypothetical pro 

 position. The establishment of laws of nature in the form of 

 reciprocal hypotheticals is an ideal at which science aims ; and 

 when we know from the subject-matter that a given hypothetical 

 is reciprocal we can derive from it the inferences just mentioned ; 

 but, apart from such knowledge, the mere form of the hypotheti 

 cal does not guarantee them. The fallacy is committed in in 

 ductive research when an hypothesis is regarded as proved by the 

 mere fact that it explains the very phenomenon to account for 

 which it was invented : it falls into the form &quot; If A then C ; but 

 C ; therefore A &quot; : an inference which is formally invalid, inasmuch 

 as it ignores the possibility of a plurality of antecedents or causes. 

 Two very common and dangerous forms of the fallacy of the 

 consequent are the assumptions (a) that we refute or disprove a 

 thesis by showing that the arguments alleged in support of it are 

 unsound (whether by reason of false premisses or of formal in 

 validity) ; () that the arguments in support of a thesis are neces 

 sarily sound (both materially and formally) because the thesis itself 

 is true (148). In regard to (a), we must remember that the only 

 way to disprove or refute a thesis is by positively proving its contra 

 dictory. Suppose that two premisses, A and , are advanced 

 in proof of a conclusion, C. He who advances the argument 

 asserts two things (i) &quot; If A and B, then C&quot; (the formal validity 

 of his syllogism), and (2) &quot; A and B are both true &quot; (its material 

 validity). Now, evidently, if we merely show that his argument 

 is formally invalid (&quot; If A and B, not necessarily C &quot;), or that 

 his premisses are not true (&quot;Not both A and B&quot;\ we do not 

 thereby establish the proposition &quot;Not C&quot;: except, indeed, the 

 combination of (i) and (2) are known to furnish the only possible 

 ground of C. Similarly, in regard to (#), we have to bear in mind 

 that a true conclusion is often defended by false or inconclusive 

 reasons a good cause is i often supported (and injured) by bad 

 arguments. A true conclusion does not guarantee the formal 

 validity of any argument that may be alleged as proving it ; nor, 

 when the argument is formally valid, does the true conclusion 

 guarantee the truth of the alleged premisses : unless these be the 

 only ones from which the conclusion in question can follow ; and 

 this latter is not guaranteed in any particular case by the mere 

 formal validity of the argument. 



