[…] the classes of 15.4 [Alternative Procedure: Classes of Morpheme-in-Environment], and any morpheme classification used for chapter 16 [Morpheme Sequences], are classes of morphemes-in environments, so that a single morpheme or morphemic sequence (or in any case a single phonemic sequence) may in one environment be a member of one class and in another environment a member of another class.
- Harris (1951), a pag.271, n.24

The morphemes are grouped into morpheme classes, or classes of morphemes-in-environments, such that the distribution of one member of a class is similar to the distribution of any other member of that class […].
- Harris (1951), a pag.363