Sucker (slang)

Gullibility is a failure of social intelligence in which a person is easily tricked or manipulated into an ill-advised course of action. It is closely related to credulity, which is the tendency to believe unlikely propositions that are unsupported by evidence.

Classes of people especially vulnerable to exploitation due to gullibility include children, the elderly, and the developmentally disabled.

The words gullible and credulous are commonly used as synonyms. Goepp & Kay (1984) state that while both words mean "unduly trusting or confiding", gullibility stresses being duped or made a fool of, suggesting a lack of intelligence, whereas credulity stresses uncritically forming beliefs, suggesting a lack of skepticism.Jewell (2006) states the difference is a matter of degree: the gullible are "the easiest to deceive", while the credulous are "a little too quick to believe something, but they usually aren't stupid enough to act on it."

Yamagishi, Kikuchi & Kosugi (1999) characterize a gullible person as one who is both credulous and naïve.Greenspan (2009) stresses the distinction that gullibility involves an action in addition to a belief, and there is a cause-effect relationship between the two states: "gullible outcomes typically come about through the exploitation of a victim's credulity."

A popular test of gullibility is to tell a friend that the word gullible isn't in "the" dictionary; a gullible person might respond "Really?" and go to look it up. Unsurprisingly, modern English language dictionaries do indeed contain the word, although some of the earliest dictionaries did not.

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