Modus Ponens - What is difference between modus ponens and modus tollens?

Two methods of deduction that provide legitimacy to certain lines of thinking are modus ponens and modus tollens. This means that 'B' must also be true (modus ponens) if 'A implies B' is correct and 'A' correct. On the other side, 'A' is false (modus tollens) if 'B' is false and 'A implies B' is true.