A bandwagon fallacy is a type of argumentative fallacy that is based on an appeal to popular belief and behavior, not on valid and logical points. An argument based on this fallacy usually bears a format similar to "everyone else believes this, so it must be true" or "everyone else does this, so it must be right." Stating that a television show is good because it has many viewers, for instance, is an example of a fallacious bandwagon argument because high viewership is not necessarily a mark of quality in and of itself. This form of argumentative fallacy can be used in many contrary situations, such as arguing that a popular claim is true or that an unpopular claim is false.
There is nothing inherently fallacious or wrong in stating that many people believe a certain proposition or act in a certain way, so long as there is truth to the statement. Such a claim becomes a logical fallacy when it is used as support for an argument. When one says "A must be true, because more people believe A than not A," one uses a bandwagon fallacy. There is nothing inherent in the beliefs of many people that can make a proposition true. When one is convinced by a bandwagon fallacy, he chooses to subordinate his own ability to think logically and examine facts to the abilities of an undefined mass of others who supposedly believe in a certain way.
While it is rare for this fallacy to be used in a formal debate, such arguments are still used in many settings, including informal arguments and marketing campaigns. Claiming that "everyone knows this is true" or "nobody believes that actually happened" saves one from actually providing evidence and support for a claim, at least if no one else involved in the argument demands further evidence. A bandwagon fallacy can be effective because it suggests that, by defying the claim, one is defying the beliefs of "everyone" or of the vast majority of people. Many people are afraid that they will seem unintelligent if they challenge a belief that is supposedly held by most people.
Marketing and advertising often make extensive use of the bandwagon fallacy. Claiming that a certain brand of a product is the "most popular" or that a certain television show is the "most viewed" is a common advertising method. People who see this use of the bandwagon fallacy may feel that, because something is popular, it is good and they will not need to conduct any more research about the product or service.