Aristotle - The Organon - index for DE INTERPRETATIONE Book 1 Part 14

Contrary and contradictory

Paragraph 1 The question arises whether an affirmation finds its contrary in a denial or in another affirmation;
Paragraph 2 Now if the spoken word corresponds with the judgement of the mind, and if, in thought, that judgement is the contrary of another, which pronounces a contrary fact, in the way, for instance, in which the judgement 'every man is just' pronounces a contrary to that pronounced by the judgement 'every man is unjust', the same must needs hold good with regard to spoken affirmations.
Paragraph 3 But if, in thought, it is not the judgement which pronounces a contrary fact that is the contrary of another, then one affirmation will not find its contrary in another, but rather in the corresponding denial.
Paragraph 4 Let me illustrate.
Paragraph 5 It is an error to suppose that judgements are to be defined as contrary in virtue of the fact that they have contrary subjects;
Paragraph 6 Now if we take the judgement that that which is good is good, and another that it is not good, and if there are at the same time other attributes, which do not and cannot belong to the good, we must nevertheless refuse to treat as the contraries of the true judgement those which opine that some other attribute subsists which does not subsist, as also those that opine that some other attribute does not subsist which does subsist, for both these classes of judgement are of unlimited content.
Paragraph 7 Those judgements must rather be termed contrary to the true judgements, in which error is present.
Paragraph 8 Now that which is good is both good and not bad.
Paragraph 9 Further, the contradictory is either always the contrary or never;
Paragraph 10 Again, the judgement that that which is not good is not good is parallel with the judgement that that which is good is good.
Paragraph 11 It is evident that it will make no difference if we universalize the positive judgement, for the universal negative judgement will form the contrary.
Paragraph 12 If therefore this is the rule with judgements, and if spoken affirmations and denials are judgements expressed in words, it is plain that the universal denial is the contrary of the affirmation about the same subject.
Paragraph 13 It is evident, also, that neither true judgements nor true propositions can be contrary the one to the other.

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