Aarne–Thompson classification system

The Aarne–Thompson classification systems are indices used to classify folktales: the Aarne–Thompson Motif-Index (catalogued by alphabetical letters followed by numerals), the Aarne–Thompson Tale Type Index (cataloged by AT or AaTh numbers), and the Aarne–Thompson–Uther classification system (developed in 2004 and cataloged by ATU numbers). The indices are used in folkloristics to organize, classify, and analyze folklore narratives and are essential tools for folklorists because, as Alan Dundes explained in 1997 about the first two indices, "the identification of folk narratives through motif and/or tale type numbers has become an international sine qua non among bona fide folklorists".

The Aarne–Thompson Tale Type Index divides tales into sections with an AT number for each entry. The names given are typical, but usage varies; the same tale type number may be referred to by its central motif or by one of the variant folktales of that type, which can also vary, especially when used in different countries and cultures. The tale type does not have to be accurate for every folktale. For example, The Cat as Helper (545B) also includes tales where a fox helps the hero. Closely related folktales are often grouped within a type. For example, tale types 400–424 all feature brides or wives as the primary protagonist, for instance The Quest for a Lost Bride (400) or the Animal Bride (402). Subtypes within a tale type are designated by the addition of a letter to the AT number, for instance: the Persecuted Heroine (510) has subtypes 510A, Cinderella, and 510B, Catskin (see other examples of tale types in the online resource links at the end of this article).

The Aarne–Thompson Motif-Index organizes thousands of motifs into a similar system. Entries are first organized by an umbrella topic (for example, category S is "Unnatural Cruelty"). Entries are then divided into more specific subcategories. For example, entry S50 "Cruel relatives-in-law", under which is the more specific entry S51.1 "Cruel mother-in-law plans death of daughter-in-law".

The AT-number system was updated and expanded in 2004 with the publication of The Types of International Folktales: A Classification and Bibliography by Hans-Jörg Uther. Uther noted that many of the earlier descriptions were cursory and often imprecise, that many "irregular types" are in fact old and widespread, and that "emphasis on oral tradition" often obscured "older, written versions of the tale types". To remedy these shortcomings Uther developed the Aarne–Thompson–Uther classification (ATU) system and included more tales from eastern and southern Europe as well as "smaller narrative forms" in this expanded listing.

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