12.231. FOR FREE FORMS [...] (i.e. for forms which sometimes constitute an utterance by themselves ). As an example, we consider many sequences ending in /s/ (e.g. 'books', 'myths') in the environments 'My — are old', 'Take the —'. We match identical sequences without /s/ ('book', 'myth') in the environments 'My — is old', 'Take the —'. Clearly, the /s/ is independent both of the preceding free form, e.g. 'book', and of anything else in the utterance. We now find that almost every sequence which ever occurs after 'The —', 'The good —', 'The old —', etc. also occurs in the environment 'The —s', 'The old —s', etc., whereas this is not true of sequences such as very which occur in 'The — good', 'The — old', etc. We conclude that /s/ (or /z/) is not merely a very common phoneme (so common that countless sequences which don’t end with 's' can be matched by otherwise identical sequences which do), but rather that the 's' is an element added on to any one of a positionally particular group of sequences. Hence both the bound /s/ (or /z/) and the various free forms to which it is added are separate elements, or morphemic segments. The morphemic status of this /s/, however, does not extend to the /s/ of box, even if we find the sequence without /s/ as in 'Bock', and even though we can match 'I’ll take the box' with 'I’ll take the Bock', because 'box' occurs in 'My — is old', rather than in 'My — are old'.
- Harris (1951), a pag.160