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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    THE ILLICIT TERM middle, the illicit processes, and the quaternio terminorum. This erroneous substitution constitutes also other fallacies, of which Traditional Logic knows nothing, since it knows nothing of the valid argument of which the fallacy is a perversion. If the roof is waterproof, we may safely infer that it is proof against rain ; but we may not infer from this postulate that it is proof against snow; for snow is not, for the purpose of the argument, equivalent to, or included in rain. If a body floats in olive oil, we may safely infer that it will float in water, for water is, for the purpose of this argument, implied in olive oil ; but if the same body will burn when soaked in olive oil, it does not follow that it will burn when soaked in water, for water is not, for the purpose of this argument, implied in olive oil. If timothy and foxtail and cocks- foot grow in this meadow, we may safely infer that couch also will grow there; but though timothy and foxtail and cocksfoot make good hay, we may not from this postulate infer that couch makes good hay; for couch, which is implied in the other grasses for the purpose of the first argument, is not implied in them for the purpose of the second. These fallacies may be termed Fallacies of the Illicit Term. It will be seen that these fallacies, while they are due to be noticed here, are properly fallacies of neglect of the purpose of the argument; and might have been dealt with, as similar fallacies have been dealt with, on a previous page. Many fallacies can, in fact, be referred to more than one class. The second Canon of Explication allows us to infer, from any postulate, all the conditions that are necessary to the postulate. No fallacy arises from failure to take advantage of the privilege a rule allows us ; but fallacy may, in this case, arise from taking, for a necessary condition, one that is not necessary. If she saw him do it, she must have been there when he did it; but this postulate does not necessarily imply, though it may be erroneously taken to imply, ‘ He must have seen her watching him.’ If there is no honey in the comb, it will not do to infer that all the honey it contained has been extracted. It may be brood-comb, and may never have contained honey. If the school did not earn the grant, it would be fallacious to argue that the teaching must have been inefficient; for that would be to assume what is not in the postulate, that inefficient teaching is a necessary condition of not earning the grant. If the fine details do not appear in this photo-