the prosecutor is as bad. If a great change in the law is proposed in Parliament, it is an Irrelevant Conclusion to argue that the proposer is not the right man to bring it forward. Everyone who gives advice lays himself open to the retort that he who preaches ought to practise, or that those who live in glass houses ought not to throw stones. Nevertheless there is no necessary connection between the character of the person giving advice and the goodness of the advice. The argumentum ad populum is another form of Irrelevant Conclusion, and consists in addressing arguments to a body of people calculated to excite their feelings and prevent them from forming a dispassionate judgment upon the matter in hand. It is the great weapon of rhetoricians and demagogues. Petitio Principii is a familiar name, and the nature of the fallacy it denotes is precisely expressed in the phrase begging the question. Another apt name for the fallacy is circulus in probando, or "a circle in the proof." It consists in taking the conclusion itself as one of the premises of an argument. Of course the conclusion of a syllogism must always be contained or implied in the premises, but only when those premises are combined, and are distinctly different assertions from the conclusion. Thus in the syllogism, B is C, therefore A is C, the conclusion is proved by being deduced from two propositions, neither of which is identical with it; but if the truth of one of these premises itself depends upon the following syllogism, C is B, therefore A is B, it is plain that we attempt to prove a proposition by itself, which is as reasonable as attempting to support a body upon itself. It is not easy to illustrate this kind of fallacy by examples, because it usually occurs in long arguments, and especially in wordy metaphysical writings. We are very likely to fall into it however when we employ a mixture of Saxon and Latin or Greek words, so as to appear to prove one proposition by another which is really the same expressed in different terms, as in the following: "Consciousness must be immediate cognition of an object; for I cannot be said really to know a thing unless my mind has been affected by the thing itself.” In the use of the disjunctive syllogism this fallacy is likely to happen; for by enumerating only those alternatives which favour one view and forgetting the others it is easy to prove anything. An instance of this occurs in the celebrated sophism by which some of the ancient Greek philosophers proved that motion was impossible. For, said they, a moving body must move either in the place where it is or the place where it is not; now it is absurd that a body can be where it is not, and if it moves it cannot be in the place where it is; therefore it cannot move at all. The error arises in the assumption of a premise which begs the question; the fact of course is that the body moves between the place where it is at one moment and the place where it is at the next moment. Jeremy Bentham however pointed out that the use even of a single name may imply a Petitio Principii. Thus in a Church assembly or synod, where a discussion is taking place as to whether a certain doctrine should be condemned, it would be a Petitio Principii to argue that the doctrine is heresy, and therefore it ought to be condemned. To assert that it is heresy is to beg the question, because every one understands by heresy a doctrine which is to be condemned. Similarly in Parliament a bill is often opposed on the ground that it is unconstitutional and therefore ought to be rejected; but as no precise definition can be given of what is or is not constitutional, it means little more than that the measure is distasteful to the opponent. Names which are used in this fallacious manner were aptly called by Bentham Question-begging Epithets. In like manner we beg the question when we oppose any change by saying that it is un-English. The Fallacy of the Consequent is better understood by the familiar phrase non sequitur. We may apply this name to any argument which is of so loose and inconsequent a character that no one can discover any cogency in it. It thus amounts to little more than the assertion of a conclusion which has no connection with the premises. Prof. De Morgan gives as an example the following: "Episcopacy is of Scripture origin; the Church of England is the only episcopal Church in England; ergo, the Church established is the Church that should be supported." By the Fallacy of the False Cause I denote that which has generally been referred to by the Latin phrase non causa pro causâ. In this fallacy we assume that one thing is the cause of another without any sufficient grounds. A change in the weather is even yet attributed to the new moon or full moon which had occurred shortly before, although it has been demonstrated over and over again that the moon can have no such effect. In former centuries any plague or other public calamity which followed the appearance of a comet or an eclipse was considered to be the result of it. The Latin phrase post hoc ergo propter hoc (after this and therefore in consequence of this) exactly describes the character of these fallacious conclusions. Though we no longer dread signs and omens, yet we often enough commit the fallacy; as when we assume that all the prosperity of England is the result of the national character, forgetting that the plentiful coal in the country and its maritime position have contributed to our material wealth. It is no doubt equally fallacious to attribute no importance to national character, and to argue that because England has in past centuries misgoverned Ireland all the present evils of Ireland are due to that misgovernment. Lastly there is the somewhat trivial Fallacy of Many Questions, which is committed by those who so combine two or three questions into one that no true answer can be given to them. I cannot think of a better example than the vulgar pleasantry of asking, “Have you left off beating your mother?" Questions equally as unfair are constantly asked by barristers examining witnesses in a court of justice, and no one can properly be required to answer Yes or No to every question which may be addressed to him. As Aristotle says, "Several questions put as one should be at once decomposed into their several parts. Only a single question admits of a single answer: so that neither several predicates of one subject, nor one predicate of several subjects, but only one predicate of one subject, ought to be affirmed or denied in a single answer." Read Prof. de Morgan's excellent and amusing Chapter on Fallacies, Formal Logic, Ch. XIII. Whately's remarks on Fallacies, Elements of Logic, Book III., are often very original and acute. LESSON XXII. THE QUANTIFICATION OF THE PREDICATE. THE syllogism has been explained in the preceding three lessons almost exactly in the form in which it has been taught for more than two thousand years. Just as Geometry has been taught in the way and order first adopted by the ancient Greek writer Euclid, so Logic has been taught nearly as Aristotle taught it about the year 335 B.C. But within the last few years teachers have at last come to the conclusion in England that Euclid's ideas of Geometry are not as perfect as could be desired. During the last 30 or 40 years also it has been gradually made apparent that Aristotle's syllogism is not an absolutely perfect system of logical deduction. In fact, certain eminent writers, especially Sir William Hamilton, Professor De Morgan, Archbishop Thomson and Dr Boole, have shewn that we need to make improvements from the very basis of the science. This reform in Logic is called by the somewhat mysterious name of the quantification of the predicate, but the reader who has found no insuperable difficulty in the preceding lessons need not fear one here. To quantify the predicate is simply to state whether the whole or the part only of the predicate agrees with or differs from the subject. In this proposition, "All metals are elements," |