A fringe theory is an idea or a viewpoint which differs from the accepted scholarship of the time within its field. Fringe theories include the models and proposals of fringe science, as well as similar ideas in other areas of scholarship, such as the humanities. In a narrower sense, the term fringe theory is commonly used as a pejorative; it is roughly synonymous with the term pseudo-scholarship. Precise definitions that make distinctions between widely held viewpoints, fringe theories, and pseudo-scholarship are difficult to construct because of the demarcation problem. Issues of false balance or false equivalence can occur when fringe theories are presented as being equal to widely accepted theories.
Fringe theories are ideas which depart significantly from a prevailing or mainstream theory. A fringe theory is neither a majority opinion nor that of a respected minority. In general, the term fringe theory is closer to the popular understanding of the word theory—a hypothesis or a guess or an uncertain idea—than to the concept of an established scientific theory. Although often used in the context of fringe science, fringe theories have been discussed in fields of scholarship, such as Biblical criticism, history, finance, law, medicine, and politics. They even exist in fields of study which are themselves outside the mainstream, such as cryptozoology and parapsychology.
Fringe theories meet with varying levels of academic acceptance. Financial journalist Alexander Davidson characterized fringe theories as "peddled by a small band of staunch supporters," but not necessarily without merit. Daniel N. Robinson described them as occupying "a limbo between the decisive dead end and the ultimately credible productive theory." However, the term is also used pejoratively; advocates of fringe theories are dismissed as cranks or crackpots who are out of touch with reality. In this sense, there is some overlap with other dismissive labels, such as pseudoarchaeology, pseudohistory, and pseudoscience.