Chapter 54

FALLACIES OF RATIOCINATION.

These fallacies (to which the name _Fallacy_ is commonly applied exclusively) would generally be detected if the arguments were set out formally; and the value of the syllogistic rules is, that they force the reasoner to be aware what it is that he is really asserting. The frequent errors in processes such as Conversion and Opposition, which are in appearance, though not in reality, inferences from premisses, may for convenience be here referred to. Such are the simple conversion of an universal affirmative; the corresponding error in a hypothetical proposition of inferring the truth of the antecedent from that of the consequent; and the confusing of a contrary with a contradictory, which amounts, in practice, to mistaking the reverse of wrong for right. But fallacies of Ratiocination properly lie in syllogisms. They commonly resolve themselves, when in a single syllogism, into the having more than three terms, whether covertly, as through an undistributed middle, or an illicit process, or avowedly. But the most dangerous and the commonest of these fallacies arise in a chain of argument from _changing the premisses_. One of the obscurer forms of this is the fallacy _a dicto secundum quid_ (i.e. with a qualification, or condition, expressed, or, more usually, understood) _ad dictum simpliciter_. Thus, the Mercantile Theory was in favour of prohibiting all trade which tends to carry out more money than it brings in, on the ground that money is riches, though it is so only if the money can be _freely_ spent. Such, too, was the argument (used to support the doctrine that tithes fall on the landlord) that, because now the rent of tithe-free land exceeds that of tithed land, the rent from the latter would be increased by the abolition of all tithes. There was a similar fallacy in the use of the maxim, that individuals are the best judges of their pecuniary interests, against Mr. Wakefield's scheme for concentrating settlers. Cases in which the condition of _time_ is dropped, fall under this same particular fallacy, as, when the maxim that prices always find their level, is construed as meaning that they are always _at_ their level. It is the same with the reasoning (especially in political and social subjects), upon principles, which are true in the absence of all modifying causes, as though no such causes _could_ exist. Other analogous fallacies are those _a dicto simpliciter ad dictum secundum quid_ (the converse of the preceding), and _a dicto secundum quid ad dictum secundum alterum quid_.