FALLACIES OF RATIOCINATION. 559 



istam notionera es. aqua tantum, et communibns et vulgaribus liquoribus, 

 absque ulla dubita verificatione, temere abstractam esse." 



Bacon himself is not exempt from a similar accusation when inquiring 

 into the nature of heat: where he occasionally proceeds like one who, seek- 

 ing for the cause of hardness, after examining that quality in iron, flint, and 

 diamond, should expect to find that it is something which can be traced 

 also in hard water, a hard knot, and a hard heart. 



The word Kii'rjnig in the Greek philosophy, and the words Generation and 

 Corruption, both then and long afterward, denoted such a multitude of 

 heterogeneous phenomena, that any attempt at philosophizing in which 

 those words were used was almost as necessarily abortive as if the word 

 hard had been taken to denote a class including all the things mentioned 

 above. Kivrftric, for instance, which properly signified motion, was taken to 

 denote not only all motion but even all change : aWoiwirig being recognized 

 as one of the modes of dvticnQ. The effect was, to connect with every form 

 of dWotwortc or change, ideas drawn from motion in the proper and literal 

 sense, and which had no real connection with any other kind of dvriaLQ than 

 that. Aristotle and Plato labored under a continual embarrassment from 

 this misuse of terms. But if we proceed further in this direction Ave shall 

 encroach upon the Fallacy of Ambiguity, which belongs to a different class, 

 the last in order of our classification. Fallacies of Confusion. 



CHAPTER VI. 



FALLACIES OF RATIOCINATION. 



§ 1. We have now, in our progress through the classes of Fallacies, ar- 

 rived at those to which, in the common books of logic, the appellation is 

 in general exclusively appropriated ; those which have their seat in the 

 ratiocinative or deductive part of the investigation of truth. Of these fal- 

 lacies it is the less necessary for us to insist at any length, as they have 

 been most satisfactorily treated in a work familiar to almost all, in this 

 country at least, who feel any interest in these speculations, Archbishop 

 Whately's Logic. Against the more obvious forms of this class of falla- 

 cies, the rules of the syllogism are a complete protection. Not (as we 

 have so often said) that ratiocination can not be good unless it be in the 

 form of a syllogism ; but that, by showing it in that form, we are sure to 

 discover if it be bad, or at least if it contain any fallacy of this class. 



§ 2. Among Fallacies of Ratiocination, we ought perhaps to include the 

 errors committed in processes which have the appearance only, not the re- 

 ality, of an inference from premises ; the fallacies connected with the con- 

 version and aequipollency of propositions. I believe errors of this descrip- 

 tion to be far more frequently committed than is generally supposed, or 

 than their extreme obviousness might seem to admit of. For example, 

 the simple conversion of a universal affirmative proposition. All A are B, 

 therefore all B are A, I take to be a very common form of error : though 

 committed, like many other fallacies, oftener in the silence of thought than 

 in express words, for it can scarcely be clearly enunciated without being 

 detected. And so with another form of fallacy, not substantially different 

 from the preceding: the erroneous conversion of an hypothetical propo- 

 sition. The proper converse of an hypothetical proposition is this : If the 



