Index for PRIOR ANALYTICS Book 1 Part 19

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Paragraph 1	If one of the premisses is necessary, the other problematic, then if the negative is necessary a syllogistic conclusion can be drawn, not merely a negative problematic but also a negative assertoric conclusion;
Paragraph 2	But if the premisses are similar in quality, when they are negative a syllogism can always be formed by converting the problematic premiss into its complementary affirmative as before.
Paragraph 3	Similar relations will obtain in particular syllogisms.
Paragraph 4	It is clear then from what has been said that if the universal and negative premiss is necessary, a syllogism is always possible, proving not merely a negative problematic, but also a negative assertoric proposition;