[…] In units consisting of more than one alternant, the total distribution of all the alternants (i.e. the combined range of environments in which each of them occurs) must equal the range of environments in which some unit with but a single alternant occurs. Thus the combined environments of 'am', 'are', 'be' are included in the environments, in which walk occurs: 'I am', 'they are', 'to be', as compared with 'I walk', 'they walk', 'to walk'.
- Harris (1942a), a pag.171