The purpose of this paper is to determine whether the sounds, ?, h, y, and w function as a natural class by investigating the following languages that have a metathesis rule affecting these sounds: Yagua, Zoque, classical Greek, Mandaic, Akkadian, Hanunoo, Tubatulabal, Twana, and Hungarian. The paper is divided into four parts. Section 1 briefly describes the rules in the nine languages chosen for the study. Section 2 explores the possibility of an implicational hierarchy of glides. Section 3 consists of some hypotheses about the motivation for metathesis, and the final section is a list of six additional languages which, because of insufficient data, are not included in the main arguments of the paper. (Author/PMP)