Aristotle - The Organon - index for DE INTERPRETATIONE Book 1 Part 10

Affirmation or denial requires a noun and a verb

Paragraph 1 An affirmation is the statement of a fact with regard to a subject, and this subject is either a noun or that which has no name;
Paragraph 2 There can be no affirmation or denial without a verb;
Paragraph 3 When the verb 'is' is used as a third element in the sentence, there can be positive and negative propositions of two sorts.
Paragraph 4 I mean that the verb 'is' is added either to the term 'just' or to the term 'not-just', and two negative propositions are formed in the same way.
Paragraph 5 Here 'is' and 'is not' are added either to 'just' or to 'not-just'.
Paragraph 6 Yet here it is not possible, in the same way as in the former case, that the propositions joined in the table by a diagonal line should both be true;
Paragraph 7 We have thus set out two pairs of opposite propositions;
Paragraph 8 This is an exhaustive enumeration of all the pairs of opposite propositions that can possibly be framed.
Paragraph 9 When the verb 'is' does not fit the structure of the sentence (for instance, when the verbs 'walks', 'enjoys health' are used), that scheme applies, which applied when the word 'is' was added.
Paragraph 10 Thus we have the propositions:
Paragraph 11 Since the contrary of the proposition 'every animal is just' is 'no animal is just', it is plain that these two propositions will never both be true at the same time or with reference to the same subject.
Paragraph 12 Further, the proposition 'no man is just' follows from the proposition 'every man is not just' and the proposition 'not every man is not just', which is the opposite of 'every man is not-just', follows from the proposition 'some men are just';
Paragraph 13 It is evident, also, that when the subject is individual, if a question is asked and the negative answer is the true one, a certain positive proposition is also true.
Paragraph 14 The propositions 'everything that is not man is just', and the contradictory of this, are not equivalent to any of the other propositions;
Paragraph 15 The conversion of the position of subject and predicate in a sentence involves no difference in its meaning.
Paragraph 16 It is evident, therefore, that the inversion of the relative position of subject and predicate does not affect the sense of affirmations and denials.

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