Aristotle - The Organon - index for ANALYTICA POSTERIORA Book 1 Part 25

Affirmative demonstration excels negative

Paragraph 1 The preceding arguments constitute our defence of the superiority of commensurately universal to particular demonstration.
Paragraph 2 (1) We may assume the superiority ceteris paribus of the demonstration which derives from fewer postulates or hypotheses - in short from fewer premisses;
Paragraph 3 Hence demonstration by fewer premisses is ceteris paribus superior.
Paragraph 4 (2) It has been proved that no conclusion follows if both premisses are negative, but that one must be negative, the other affirmative.
Paragraph 5 (3) The basic truth of demonstrative syllogism is the universal immediate premiss, and the universal premiss asserts in affirmative demonstration and in negative denies:
Paragraph 6 (4) Affirmative demonstration is more of the nature of a basic form of proof, because it is a sine qua non of negative demonstration.

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