Analysis of information sources in references of the Wikipedia article "Aarne–Thompson–Uther Index" in English language version.
Negative or skeptical views of the possibility of classifying folklore material on a typological basis find support in the fact that the classification systems successfully applied to European folklore material have not proved valid for material from other continents.
Stith Thompson, arguably the greatest American folklorist of the 20th century, ... Thompson's prudishness comes as no surprise when one recalls that he bothered to write a special footnote to his entry Motif X 700, Humor concerning sex. In what was supposed to be a comprehensive six-volume worldwide listing of folk-narrative motifs, he does not list so much as a single bibliographical citation for this category.