Let A be the claim and M an impossible consequence. The pattern is:
1. Assume not-A.
2. Establish from premises: If not-A, then M.
3. M is impossible, so M is false.
4. Therefore not-A is false.
5. By the rule of contradictories, A is true.
Step 2 belongs to the connected hypothetical argument, steps 3–4 to the exceptive inference, and step 5 applies the principle of contradiction.
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Qiyās al-Khalf: Compound Reductio, Impossibility and Proof of the Claim
Let A be the claim and M an impossible consequence. The pattern is:
1. Assume not-A.
2. Establish from premises: If not-A, then M.
3. M is impossible, so M is false.
4. Therefore not-A is false.
5. By the rule of contradictories, A is true.
Step 2 belongs to the connected hypothetical argument, steps 3–4 to the exceptive inference, and step 5 applies the principle of contradiction.