Aristotle - The Organon - index for DE INTERPRETATIONE Book 1 Part 7

Universal and individual subjects

Paragraph 1	Some things are universal, others individual.
Paragraph 2	Our propositions necessarily sometimes concern a universal subject, sometimes an individual.
Paragraph 3	If, then, a man states a positive and a negative proposition of universal character with regard to a universal, these two propositions are 'contrary'.
Paragraph 4	An affirmation is opposed to a denial in the sense which I denote by the term 'contradictory', when, while the subject remains the same, the affirmation is of universal character and the denial is not.
Paragraph 5	We see that in a pair of this sort both propositions cannot be true, but the contradictories of a pair of contraries can sometimes both be true with reference to the same subject;
Paragraph 6	When, on the other hand, the reference is to universals, but the propositions are not universal, it is not always the case that one is true and the other false, for it is possible to state truly that man is white and that man is not white and that man is beautiful and that man is not beautiful;
Paragraph 7	This statement might seem at first sight to carry with it a contradiction, owing to the fact that the proposition 'man is not white' appears to be equivalent to the proposition 'no man is white'.
Paragraph 8	It is evident also that the denial corresponding to a single affirmation is itself single;
Paragraph 9	For instance, the affirmation 'Socrates is white' has its proper denial in the proposition 'Socrates is not white'.
Paragraph 10	The denial proper to the affirmation 'every man is white' is 'not every man is white';
Paragraph 11	We have shown further that a single denial is contradictorily opposite to a single affirmation and we have explained which these are;