Affirming a disjunct

Name of fallacy Affirming a disjunct
Type Deductive Argument, Formal Argument
Description Concluding that one logical disjunction must be false because the other disjunct is true
FormA or B; A; therefore not B.
Treatment The error is assuming that the premises are mutually exclusive. A and B could both be true. Show that they can both be true and therefore that the conclusion does not stand.