Hypothetical syllogism
Transformation rules 

Propositional calculus 
Rules of inference 
Rules of replacement 

Predicate logic 
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.^{}^{}
 If I do not wake up, then I cannot go to work.
 If I cannot go to work, then I will not get paid.
 Therefore, if I do not wake up, then I will not get paid.
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 nonclassical logic. The rule may be stated:
where the rule is that whenever instances of "", and "" appear on lines of a proof, "" can be placed on a subsequent line.
Hypothetical syllogism is closely related and similar to disjunctive syllogism, in that it is also type of syllogism, and also the name of a rule of inference.
Formal notation
The hypothetical syllogism rule may be written in sequent notation:
where is a metalogical symbol meaning that is a syntactic consequence of , and in some logical system;
and expressed as a truthfunctional tautology or theorem of propositional logic:
where , , and are propositions expressed in some formal system.
See also
References
External links
 Philosophy Index: Hypothetical Syllogism