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Equivocation (or the magician's choice) is a verbal technique by which a magician gives an audience member an apparently free choice, but frames the next stage of the trick in such a way that each choice has the same end result. For example, the performer may deal two cards to the table and ask a spectator to select one: if the spectator chooses the card on the left, the performer will say something like "you keep this card, I'll take the remaining card". If the spectator chooses the card on the right, the performer will take that card. Thus, the choice of which card to use is really made by the magician.
These basic techniques can be expanded to include practically any number of items, such as an entire deck of cards. For larger sets, items may first be grouped, then split up. The magician must quickly and carefully craft patter to convey the impression that the actions he or she takes with the items truly reflect the intent of the spectator.
Equivocation can be used to force a card without the use of sleight of hand. The use of this kind of verbal force in close-up magic apparently offers a subject a free or random choice of card. It is not as common as sleight of hand or other methods.
In another use, a mentalist may perform an apparent act of mind reading by using the "magician's choice" to force a particular envelope that relates to a needed outcome. A mentalist may also force an effect from a certain outcome, as in taking something ordinary and using it to show their magical prowess.
In each of these examples, the effectiveness of the equivocation involves the "information gap" between what the spectator knows and what the spectator thinks they know. In the magician's force, the spectator does not know anything about what will happen to the two cards he initially selects. However, the spectator thinks that they are making a free choice in an otherwise scripted sequence of moves. In the effect of the prepared envelope, the spectator thinks they know that the envelope involves a prediction, but does not realize that the envelope in fact involves three predictions.
Equivocation tends to lose its effectiveness if repeated in the same context, since the spectator gains more information from one performance to the next, thereby shrinking the information gap. For example, a spectator may wonder why their choice was kept in some cases and discarded in others. Equivocation is a particular form of alternate ending forces where double entendre wording is used and a different pattern of results to questions can be noticed, but its real strength is best realized when augmented with artful psychological techniques.