A new logic / by Charles Mercier.

  • Mercier, Charles Arthur, 1852-1919.
Date:
1912
Catalogue details

Licence: In copyright

Credit: A new logic / by Charles Mercier. Source: Wellcome Collection.

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    bear, or a centaur, or a phoenix, or a jabberwock. Whether parsley is or is not, in experience, fatal to parrots, is as irrelevant and out of place in the one argument, as whether white bears, or centaurs, or phoenixes, or jabberwocks, really exist, is irrelevant and out of place in the other ; or as whether Socrates really is or is not mortal is out of place and irrelevant in the syllogism. Almost every logician points out that the conclusion of a syllogism may be true, though its premisses are false. All large glass bottles are covered with the craters of volcanoes ; The moon is a large glass bottle; /. The moon is covered with the craters of volcanoes. In this case, the conclusion happens to be true, though the truth of the premisses leaves something to be desired; and instances to the same effect are adduced by most logicians; who, neverthe- less, on another page, blandty assure us that the truth of the con- clusion depends on the truth of the premisses. A just appreciation of the nature of Deduction would have shown them that it is not permissible even to discuss the truth of the conclusion of an Inference. We might as well discuss whether it is white or black, transparent or opaque. Inference is not concerned with material truth. It is concerned solely with consistency, and to discuss the truth of its conclusions is fallacious. It is a fallacy of Confusion of the Modes of Reasoning. It is this confusion of the argument in materia with the argument from postulates that constitutes the fallacy of supposing that, if a man’s reasoning is consistent, his conclusions must be true that since his conclusions are true, his reasoning must be valid ; that if we can find a flaw in his reasoning, his conclusion must be false; and that if his conclusions are not true, his reasoning must be invalid. All these are fallacies not infrequently perpetrated ; none of them is enumerated among the fallacies of the Sophistici Elenchi, or in any subsequent chapter on fallacies. They eluded even the vigilant and penetrating eye of De Morgan ; but they are brought to light by the system of Logic here expounded. The problem of the pelitio principii in the syllogism is put in various ways in books of Logic. It is put variously: If all men are mortal, and Socrates is a man, how do we know that Socrates is