Hypothetical syllogism

In classical logic, hypothetical syllogism is a valid argument form which is a syllogism having a conditional statement for one or both of its premises.

In propositional logic, hypothetical syllogism is the name of a valid rule of inference (often abbreviated HS and sometimes also called the chain argument, chain rule, or the principle of transitivity of implication). Hypothetical syllogism is one of the rules in classical logic that is not always accepted in certain systems of non-classical logic. The rule may be stated:

where the rule is that whenever instances of "${\displaystyle P\to Q}$", and "${\displaystyle Q\to R}$" appear on lines of a proof, "${\displaystyle P\to R}$" can be placed on a subsequent line.

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