Boas's rejection of Morgan's theories led him, in an 1887 article, to challenge Mason's principles of museum display. At stake, however, were more basic issues of causality and classification. The evolutionary approach to material culture led museum curators to organize objects on display according to function or level of technological development. Curators assumed that changes in the forms of artefacts reflect some natural process of progressive evolution. Boas, however, felt that the form an artefact took reflected the circumstances under which it was produced and used. Arguing that "[t]hough like causes have like effects, like effects have not like causes", Boas realized that even artefacts that were similar in form might have developed in very different contexts, for different reasons. Mason's museum displays, organized along evolutionary lines, mistakenly juxtapose like effects; those organized along contextual lines would reveal like causes.