The number of morpheme classes would vary according as we use no approximation, or little, or much.
- Harris (1951), a pag.244, n.6

These morpheme classes are elements of the language description not only by virtue of their definition, but also in the sense that many of them are characterized by special features common to all their member morphemes. In this sense we may even say that many morpheme classes (or, in some cases, sub-classes) have a common class meaning. In many languages we find that the distributionally determined classes (of morphemes, or morpheme sequences) have meanings which we may roughly identify as ‘noun’, ‘verb’, ‘preposition’, etc. Even classes of morpheme classes may have vague meaning characteristics. For example, in many languages the free morphemes (of whatever class) may be said to indicate objects, actions, situations, and the like, while the short bound morphemes (again of whatever class) indicate relations among these, times and persons involved, and the like.
- Harris (1951), a pag.252, n.21

A single morpheme class, which may be substitutable for a sequence of morpheme classes, is considered a special case of a sequence.
- Harris (1951), a pag.263, n.2

In some cases we find a class of morphemes which occurs only with another class, which in turn occurs only with the first class. For example, the 'wh-' of 'why', 'when', 'where', 'which', is clearly a separable morpheme (cf. 'then', 'there'), and occurs in a fairly large number of positions (at the beginning of certain questions and of 'N', before or after 'V', etc.) But whenever it occurs it always has one of a very few morphemes ('-en', '-ere', '-ich', etc.) after it. These morphemes, in turn, occur only after 'wh-' and after a few other morphemes (chiefly 'th-', which is not in the same class as 'wh-' because its utterance position is different), so that they form a small special class occurring in very limited sequences.
- Harris (1951), a pag.268

We may find that in one language there are certain large morpheme classes each of which occurs only in sequences equated to a corresponding position class (e.g. a language with different noun stems occurring in noun position and verb stems in verb position). In another language there may be one large morpheme class which is equated to various position classes by occurring in sequences with various small morpheme classes of bound forms (e.g. Hidatsa, where almost any stem occurs in noun position if 's' is added to it, and in verb position if 'c' is added to it). In the latter case we may say that the utterance status is borne by affix classes which themselves never equal a position class but operate on other classes (stem) which are by themselves positionally neutral. There is no noun class in Hidatsa, only a stem class (neither noun nor verb), a class of nominalizing suffixes, and a class of verbalizing suffixes.
- Harris (1951), a pag.277

Constructions and other domains may correlate with particular morpheme classes in a sufficiently general manner to merit special note. For example, a number of morpheme classes may appear together in various combinations, but never in constructions with other morpheme classes. The constructions in which the former participate may differ in many respects from the other constructions. This is often the case in languages which have a large stock of morphemes borrowed from foreign sources with some of the grammar of their original language, e.g. English words of Latin and Greek derivation. Many of these constructions and classes may occur primarily in special styles or social dialects of the language, e.g. the use of the above English vocabulary in learned speech and in writing.
- Harris (1951), a pag.346

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 […]. These morpheme classes and any sequences of morpheme classes which are substitutable for them within the utterance […], are now grouped into larger classes (called position or resultant classes) in such a way that all the morpheme sequences (including sequences of one morpheme) in a position class substitute freely for each other in those positions in the utterance within which that class occurs.
- Harris (1951), a pag.363

It will in general be found that very few morpheme classes remain on the right side of the equations, without being included in some sequence which is equated to some other morpheme class. We thus come out with a few classes (each having its highest raised number […]), e.g. 'N⁵, V⁴, D', and several contours, to some one or another of which every morpheme sequence is equivalent. Any utterance can be described as a sequence of these few remaining classes, since any sequence in the utterance can be equated to one or another of these: 'These hopeful people want freedom' is 'NV' because 'these is' 'TA', 'hopeful' is 'N Na = A', 'freedom' is 'A An = N', and 'TAAN = TAN = TN = N', and 'VN = V' ('see it' for 'see' in 'I — now.'). (p.274)
- Harris (1951), a pag.274