In
logic, a
rule of inference,
inference rule or
transformation rule is a
logical form consisting of a function which takes premises, analyzes their
syntax, and returns a conclusion (or
conclusions). For example, the rule of inference called
modus ponens takes two premises, one in the form "If p then q" and another in the form "p", and returns the conclusion "q". The rule is valid with respect to the semantics of
classical logic (as well as the semantics of many other
non-classical logics), in the sense that if the premises are true (under an interpretation), then so is the conclusion.