An Essay on Reasoning (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1891 edition. Excerpt: ...which do not shine by reflected light are identical with some bodies which shine by their own light. And as the formal shape of the second premise is only--The sun is identical with some body which shines by its own light the conclusion involves a fallacy of the undistributed middle. Of course if the alternatives in the first premise were intended to be exclusive, the conclusion would be sound. Before leaving this part of the subject, I must briefly refer to the more important argumentative fallacies, as opposed to those which are contained in the syllogism itself. These are commonly called semi-logical and material fallacies. The fallacies classed under the former head are all different kinds of ambiguity, and do not deserve any special mention beyond what I have already said on the subject. I have already, in the first chapter, noticed the two principal material fallacies, namely, Non sequitur and petitio principii. The fallacy of 'Accident' has been described as ' arguing erroneously from a general rule to a special case.' This definition itself contains a curious petitio principii, for to say it is a fallacy to do something erroneously, is merely begging the question. The truth of the matter is that if it was a fallacy to argue to the special case, then it was a falsehood to state the general rule without exception. Such falsehoods, or perhaps I might say inaccuracies of expression, are the causes of this fallacy. Aristotle deduced his whole theory of the syllogism from such a general rule, his dictum de omni et nullo, namely, What is true of all is true of each considered separately. This dictum would of course justify any fallacy of accident; and this shows the absurdity of calling such dicta laws of thought, ...