There is little difference between fallacies like (1) and fallacies of converse accident. Concerning illustration (2), both statements are false; but to contradict we know that if one is false, the other must be true.
(2) Obversion.
“Two negatives are equivalent to one affirmative,” is the principle underlying obversion. The most common fallacy in obversion springs from using one negative instead of two.
ILLUSTRATIONS OF FALLACIOUS OBVERSION.
(a) Original: Some men are not wise. Obverse: (incorrect) Some men are wise.
(b) Original: All true teachers are just. Obverse: (incorrect) All true teachers are not just.
(3) Conversion.
Conversion involves the interchanging of the subject and predicate of a proposition without affecting the distribution; in consequence the usual fallacy incident to this interchange is distributing an undistributed term.
ILLUSTRATIONS OF FALLACY OF CONVERSION.
(a) Original: All fixed stars are heavenly bodies. Converted: (incorrectly) All heavenly bodies are fixed stars.