 In Qiyās VII.1, Avicenna considers a basic set of quantified conditional statements with quantified antecedents and consequents. Assuming the four basic forms of quantified conditional statements (a-\(\mathbb{C}\)), (e-\(\mathbb{C}\)), (i-\(\mathbb{C}\)), and (o-\(\mathbb{C}\)) and all permutations of a-, e-, i-, o-propositions as antecedents and consequents, Avicenna generates four groups of sixteen conditional propositions (see  Appendix B)  and argues that any of those forms is logically equivalent to the contradictory conditional with a contradictory consequent, based on a reductio proof that may easily be generalized. As illustrated above (contradiction of conditional propositions), the (a-\(\mathbb{C}\))aa proposition is for instance equivalent to the (e-\(\mathbb{C}\))ao proposition (“Always, if every A is B, then every C is D” if and only if “Never, if every A is B, then not every C is D”). If that were not the case, then (i-\(\mathbb{C}\))ao would be true. But then (o-\(\mathbb{C}\))aa would be true, which contradicts the initial assumption. For an account of Avicenna’s reductio proof of the fact that “Always, if every A is B, then every C is D” implies “Never, if every A is B, then not every C is D”—at Qiyās 367.11–368.1—see (El-Rouayheb 2009: 209–210 and 2010:  xxxiii–xxxiv).[11]