§ 842. The Fallacies of Undistributed Middle and Illicit Process have been treated of under §§ 585, 586. The heading 'Negative Premisses and Conclusion' covers violations of the three general rules of syllogism relating to negative premisses (§§ 590-593). Here is an instance of the particular form of the fallacy which consists in the attempt to extract an affirmative conclusion out of two negative premisses—
All salmon are fish, for neither salmon nor fish belong to the class mammalia.
The accident of a conclusion being true often helps to conceal the fact that it is illegitimately arrived at. The formal fallacies which have just been enumerated find no place in Aristotle's division. The reason is plain. His object was to enumerate the various modes in which a sophist might snatch an apparent victory, whereas by openly violating any of the laws of syllogism a disputant would be simply courting defeat.
§ 843. We now revert to Aristotle's classification of fallacies, or rather of Modes of Refutation. We will take the species he enumerates in their order, and notice how modern usage has departed from the original meaning of the terms. Let it be borne in mind that, when the deception was not in the language, Aristotle did not trouble himself to determine whether it lay in the matter or in the form of thought.
§ 844. The following scheme presents the Aristotelian classification to the eye at a glance:—
| |—Equivocation.
| |—Amphiboly.
|—In the language -|—Composition.
| |—Division.
| |—Accent.
| |—Figure of Speech.
Modes of -|
Refutation. | |—Accident.
| |—A dicto secundum quid.
| |—Ignoratio Elenchi.
|—Outside the language -|—Consequent.
| |—Petitio Principii.
| |—Non causa pro causa.
| |—Many Questions.
[Footnote: for "In the language": The Greek is [Greek: para ten lexin], the exact meaning of which is; 'due to the statement.']
§ 845. The Fallacy of Equivocation [Greek: òmonumía] consists in an ambiguous use of any of the three terms of a syllogism. If, for instance, anyone were to argue thus—
No human being is made of paper,
All pages are human beings,
.'. No pages are made of paper—
the conclusion would appear paradoxical, if the minor term were there taken in a different sense from that which it bore in its proper premiss. This therefore would be an instance of the fallacy of Equivocal Minor.