Logically enough, the new rule is called modus tollens and its annotation is just ‘MT’. Certainly, MT yields a negated conclusion but only if we already have a negated formula, i.e. MT transfers negation from consequent to antecedent. Logically enough, when we negate a negation we produce what’s called a double negation. Many logicians delight in deducting marks from students who fail to make use of double negation-introduction to enable the proper application of MT. Although this is a relatively minor logical sin it is a logical sin none the less. Logically enough, inclusive disjunction contrasts with exclusive disjunction, which excludes the possibility that a disjunction is true when both its disjuncts are true. Either way, a disjunction is true if even one of its disjuncts is true.