1. A NEGATIVE ASPECT.
It has been remarked that “Logic as a science makes known the laws and forms of thought and as an art suggests conditions which must be fulfilled to think rightly.” In recent chapters we have discussed the second aspect of the definition; in these we have attempted to answer the question, “What rules must be followed in order to reason correctly?” We are now ready to treat the same aspect from a negative point of view namely, what errors must be avoided in order to reason correctly? What are the fallacies which we must strive to avoid in our own thinking, and attempt to correct in the thinking of others?
2. PARALOGISM AND SOPHISM.
“Fallacy” comes from the Latin fallacia, meaning deceptive or erroneous, and therefore a fallacy in logic is any error in reasoning which has an appearance of correctness. If the writer or speaker is himself deceived by the fallacy, then such is called a Paralogism; but if the fallacy is committed by him for the expressed purpose of deceiving others, then such becomes a Sophism. During the time of the Schoolmen the Sophism was in such high repute that it required even a Socrates to puncture this ignominious bubble of vain trickery. In fact, Socrates, the greatest of all pagan educators, led the crusade whichhas relegated to the “logical dust bin” the notion that skill in the art of framing sophisms is a scholarly accomplishment. Many believe modern sophistry to be the chief social and commercial evil of the day, and to Socrates must be given the credit for teaching us to look upon those who would practice sophism with righteous indignation and pronounced disgust. However, paralogism and not sophism is the more legitimate field for the student of logic; his problem being, “What are the common errors which I, as a writer and speaker, must strive to avoid?”
3. A DIVISION OF THE DEDUCTIVE FALLACIES.
The mistakes of induction will occupy our attention in a later chapter. We are now concerned with the fallacies of deduction. Any classification or division of the deductive fallacies must of necessity be faulty. Even the labors of Aristotle in this regard are now pronounced crude and unsatisfactory. This is due to the divergence of opinion as to the signification of some of the fallacies, as well as to the fact that no division is free from the fault of an overlapping of the species. As a result of this lack of unanimity in definition and lack of ability in making the species mutually exclusive, any division of the deductive fallacies must be more or less illogical.
Aristotle divides the fallacies of deduction into two groups: (1) Fallacies in dictione, or formal fallacies. (2) Fallacies extra dictionem, or material fallacies. This division has received universal approval and though many distinctions made by him have been abandoned, yet most logicians retain his phraseology. Since many of the technicalterms which Aristotle used have lived through the generations under the conventional meaning which he assigned to them, it becomes less confusing to adhere as closely as possible to these terms. Therefore, in the attending division only those changes have been made which progress and experience have forced upon us. What remains of this chapter will be devoted to explaining these fallacies as they appear in this division. For the sake of clearness and definiteness it is strongly recommended that the student study the outline extensively enough to be able to reproduce it.
| Formal (In dictione) | ||
|---|---|---|
| 1. Immediate inference |  | 1. Opposition |
| 2. Obversion | ||
| 3. Conversion | ||
| 4. Contraversion | ||
| 2. Categorical arguments | | 5. Four terms |
| 6. Undistributed middle | ||
| 7. Illicit major | ||
| 8. Illicit minor | ||
| 9. Negative premises | ||
| 10. Particular premises | ||
| 3. Hypothetical arguments | | 11. Denying the antecedent |
| 12. Affirming the consequent | ||
| 4. Disjunctive arguments | | 13. Illogical disjunction |
| Material (In dictionem) | ||
| 1. In Language Equivocation | | 1. Ambiguous middle |
| 2. Amphibology | ||
| 3. Accent | ||
| 4. Composition | ||
| 5. Division | ||
| 6. Figure of speech | ||
| 2. In Thought Assumption | | 1. Accident |
| 2. Converse accident | ||
| 3. Irrelevant conclusion | ||
| 4. Non sequitur | ||
| 5. False cause | ||
| 6. Complex question | ||
| 7. Begging the question | ||
4. GENERAL DIVISIONS EXPLAINED.
The formal fallacies are those which concern the form of the argument rather than the meaning.These fallacies arise from an improper use of words as arbitrary signs of thought, not from any inconsistency in the thought itself. To commit a formal fallacy we must violate one of the specific rules of logic. For this reason the formal fallacies are easier of comprehension. Moreover, because of this definiteness logicians are better able to come to some agreement as to their content and import. Classing the fallacies of immediate inference as formal is somewhat of an innovation; but since they occur because of the breaking of certain definite rules, and since immediate inference is a matter of changing the form without altering the meaning, we believe there is some justification for this position. Some would class “immediate inference” fallacies with the material fallacies of language.