Define Modus Tollens.

Modus Tollens is a valid form of deductive reasoning in classical logic. It is a Latin term that means "mode that denies" or "method of denying." The structure of Modus Tollens involves a conditional statement and its contrapositive. The logical form is as follows:

1. If P, then Q. (P → Q)
2. Not Q. (¬Q)
3. Therefore, Not P. (¬P)

In other words, if a conditional statement "If P, then Q" is true, and it is known that Q is false (¬Q), then it logically follows that the antecedent P must also be false (¬P). Modus Tollens is effective in affirming the negation of the antecedent when the consequent is shown to be false.

For example:

1. If it is raining (P), then the ground is wet (Q). (If P, then Q)
2. The ground is not wet (¬Q).
3. Therefore, it is not raining (¬P).

Modus Tollens is a cornerstone of deductive reasoning and plays a crucial role in establishing logical conclusions based on the negation of the consequent.