Morphology, broadly, is the study of form or structure. Folkloristic morphology, then, is the study of the structure of folklore and fairy tales.
Antti Aarne's theories, enlarged and expanded by American folklorist Stith Thompson in 1961 and by Hans-Jörg Uther in 2004, look at motifs rather than actions – for example, "a soldier makes a deal with the devil" or "a soldier marries the youngest of three sisters". More than 2500 folk and fairy tales have been cataloged under this taxonomy; the AaTh or Aarne–Thompson number is as well-known to folklorists as Francis James Child's identification of ballads are to scholars of folk songs.
Vladimir Propp was a Russian structuralist scholar. He criticized Aarne's work for ignoring what motifs did in a tale, and analysed the basic plot, or action, components of Russian folk tales to identify their simplest irreducible narrative elements. His Morphology of the Folk Tale was published in Russian in 1928 and influenced Claude Lévi-Strauss and Roland Barthes, though it received little attention from Western scholars until it was translated into English in the 1950s.
In the Afanasyev's collection of Russian fairy tales, Propp found a limited number of plot elements or "functions" that constructed all. These elements occurred in a standard, consistent sequence. He derived thirty-one generic functions, such as "a difficult task is proposed" or "donor tests the hero" or "a magical agent is directly transferred".