A rule of inference, inference rule, or transformation rule is a tool used in logic. A rule of inference can take one or more statements, called premises, and return some other statement, called a conclusion. 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, in the sense that if the premises are true, then so is the conclusion.