Slight of mouth, a vernacular cousin to the magician's slight of hand, was created in the mid 1970s by the founders of neuro-linguistic programming — a tool for persuading people to change their beliefs and do what others want them to do. Consisting of 14 precise ways to respond to others, slight of mouth is often used by politicians, business leaders and therapists who want what they say should happen to actually come about. Often this involves challenging the logical foundation of someone's beliefs in an effort to quickly gain footing in a debate.
The magic of slight of mouth involves breaking down a person's assertions into two main categories. First, a person may state that since one thing is true, then something else should be true — a train of equivalent logic that may or may not be valid. This will follow an "A = B" format in formal logic, with A and B being two separate ideas. For instance, "You were the last person to turn in the test, so you were probably the least prepared of the class."
Another target of slight of mouth is the assertion of cause and effect. These are made when someone wants to convey that one thing causes, or was caused, by something else. For instance, patient may tell a psychiatrist, "I'm depressed a lot because I don't feel like anybody ever listens to me."
There is a slight of mouth retort for any statements made in these two veins. Employing them, however, does not ensure victory in a debate or argument. These replies are aimed at poking holes in a person's armor of resolve, pointing out illustratively the often hidden and outright logical fallacies in a person's beliefs.
The first slight of mouth pattern involves the intent of the speaker. In response to the first equivalent statement about turning the test in last, a respondent may say, "You were always looking out for me." To the cause and effect statement about being depressed, the psychiatrist may alter the patient's outlook by asking, "What are you doing to make better friends?"
A complete description of each of the 14 slight of hand formats, with examples, is readily available online. They include challenging consequences, pointing out other outcomes, offering a counter-example, applying the statement to the speaker, challenging the veracity of the statement, pointing out erroneous metaphor, and changing the scale of the statement. Other categories include upping the logical ante, pointing out specific errors, going to a general level from the specific, offering an example to illustrate the fallacy, and restating the original comment in a more outlandish way. The rest of the 14 are uprooting the statement from its current place in history and shifting focus by asking what moral or logical belief has led the speaker to make such a comment.