[…] the fundamental criterion in grouping morphemic elements is to set up such morphemes in terms of which compact general statements concerning the composition of the utterance of our corpus can be made. It is therefore desirable that the morphemes should be made as distributionally similar to each other as possible, or that there should be groups of morphemes having identical distributions. This is not a difficult criterion to satisfy, because we will find in a great many cases […] that there are whole groups of morphemic segments each of whose total distribution […] is almost identical with that of every other segment in the group.
- Harris (1951), a pag.201