§ 4. III. The fallacy of Irrelevancy (or, as it is sometimes called, shifting ground) is technically termed Ignoratio Elenchi, i. e. ignorance of the syllogism required for the refutation of an adversary. Thus, in the strictest sense of the words, ignoratio elenchi is committed by a person who in a disputation does not confine himself to proving the contradictory or contrary of his adversary's assertion, or who proves a proposition other than the contradictory or contrary. But, like many other terms borrowed from the dialectical disputations of the ancients, this has now received a wider meaning. Whenever an argument is irrelevant to the object which a speaker or writer professes to have in view, it is called an ignoratio elenchi. Thus, if I am endeavouring to convince a person that some particular measure is for his personal interest, and I adduce arguments to prove that it contributes to the general utility, or that it is the necessary consequence of other acts of legislation, I am guilty of an ignoratio elenchi, as I should also be if, when it was my object to establish either of the other two conclusions, I were to appeal to his personal interest. When the question at issue is the truth of an opinion, it is an ignoratio elenchi to attack it for its novelty, or for its coming from a foreign source, or for any supposed consequences which may result from it, or to try to throw discredit on its author by saying that it has often been started before, and so is no discovery of his.

This fallacy is more common in spoken addresses than in books, as the feelings both of speaker and hearers

being more excited, and their judgment less critical, they are less likely to insist on relevancy of argument. On such occasions it most commonly takes the form of an argumentum ad hominem, whereby the speaker, in support of the truth of his assertions, or to throw discredit on an adversary, appeals, not to the unbiassed judgment of his auditors, but to their passions, interests, prejudices, sentiments and associations. The argumentum ad hominem, however, is not confined to set speeches; it sometimes occurs in writings, and frequently in debates. In the latter, it often assumes the shape of an appeal to the previous acts, or the previously expressed convictions of the opponent; 'That measure, or that argument, or that proposal does not come well from you, who once proposed such a measure, or expressed such an opinion, or advanced such an argument, or did such and such acts.' There are occasions when the argumentum ad hominem may legitimately be used as a retort, but it must be advanced as such, and not as an argument. It is so called in opposition to the argumentum ad rem or ad judicium. Similar phrases are used to express other forms of the ignoratio elenchi, as e. g. the argumentum ad verecundiam, argumentum ad baculum, &c. The argumentum ad populum I have treated as identical with the argumentum ad hominem; if called on to distinguish them, which seems unnecessary, I should refer the first to addresses made in the presence of a large auditory, the second to disputations with one or a few individuals 3.

5 The student will find some amusing examples of ignoratio

5. IV. The fallacy originating in ambiguity of language I noticed when warning the student against the employment of equivocal terms. This fallacy (whether we call it that of equivocal terms, of ambiguous terms, or of ambiguity of language) of course includes fallacies arising from any ambiguity which may attach to the quantity of the subject, as e. g. the fallacy arising from the ambiguous use of the word 'all,' which will be noticed below.

I now proceed to notice one or two common cases of this fallacy. The same term may often be used in one place distributively and in another collectively, and we may argue as if the term in both places had the same meaning. This is called the fallacy of Combosition or Division; of composition, if we argue from a term taken distributively as if it were taken collectively; of division, if we argue from a term taken collectively as if it were taken distributively. Thus (to give common instances) 7 and 2 are (distributively) odd and even, nine is 7 and 2 (collectively); ... nine is odd and even. Here we argue from 7 and 2 taken distributively, as if they had been taken collectively, and the fallacy is one of composition. Five is one number, 3 and 2 (collectively) are five; .. 3 and 2 (distributively) are one number. Here the fallacy is one of division. Again, The people of England have a prejudice against the French, he is one of the people of England; ... he has a prejudice

elenchi, or irrelevant argument, in Sydney Smith's well-known jeu d'esprit, the Noodle's Oration.

against the French. The major premiss might be quite true, and still the particular man spoken of might have French, and be a warm Here we argue from the

a strong sympathy with the admirer of their institutions. term 'people,' taken collectively, as if it had a distributive signification and whatever were predicable of the English people might be predicated of every single individual amongst them; hence the fallacy is one of division. The last instance is an example of a very common source of deception. A certain people, corporation, or society, in its collective capacity, has certain characteristics, has performed certain acts, passed certain resolutions, or is known to have expressed certain sentiments; hence it is unreflectingly supposed that any particular individual belonging to the class has the same characteristics, participates in the same sentiments, and has joined in the same acts. In many cases, of course, he may be a strong dissentient, and may have actively opposed the measures adopted.

The ambiguous use of the word 'all' furnishes a good instance of the fallacies of composition and division. We may argue from 'all,' meaning all taken together, as if it meant all severally, and thus commit the fallacy of division; or from 'all,' meaning all severally, as if it meant all taken together, and thus commit the fallacy of composition. Thus, when I say, 'All these boxes weigh so much,' or 'All these men can eat so much,' I leave it doubtful whether I mean all taken together or all taken severally. The ambiguity may be removed by substituting

for the word 'all,' when used in a distributive sense, 'every,' and, when used in a collective sense, 'the whole of.'

Another pair of fallacies which falls under the head of 'ambiguous terms' is the pair known as the Fallacia Accidentis (or the Fallacia a dicto simpliciter ad dictum secundum quid) and the Fallacia a dicto secundum quid ad dictum simpliciter. In the first we argue from what is true as a general rule (i. e. unless there be some modifying circumstances) as if it were true under all circumstances; in the second from what is true under certain special circumstances as if it were true as a general rule. Thus a particular walk may be an agreeable one, but it does not follow that it would be so in wet or windy weather; plain-speaking, frugality, generosity, may all be virtues, but it does not follow that it would be virtuous to practise them on all possible occasions. Or, to take instances of the second fallacy, a political revolution may, under particular circumstances, be necessary to the welfare or existence of a country, but it does not follow that a state of society, in which political revolutions are frequent, is either necessary or desirable; it may be necessary if I am suffering from a particular disease that I should take opium or abstain from labour, but it does not follow that these practices would be good for me when I am restored to health. The fallacies are due to our not sufficiently qualifying the terms which we use, and, by insisting on precision of language, they may always be avoided.