As it was shown in§15 Morphology is to be defined in two ways: according to the units described in it and according to properties of the units.
You know since your school years that morphology studies words. It is true. But this is not the whole truth. Morphology, when translated from Greek, means “study of form”. In Language studies it means “forms of words”. This definition complies both with the meaning of the Greek word “morfologia” and the definition of Grammar we follow. Because Grammar (of a language) is a system for showing meanings through opposition of variants of units, which variants in this case become (grammatical) forms, grammatical Morphology is a system of forms of words. If so, the definition of Grammar as an activity to understand and describe a language should be as formulated above: Grammar is a study of forms of words.
This definition permits us to calculate those elements that are to discussed in this part of Grammar. Since forms of words morphemes these units are also to included into this study. Because forms of words are built to show certain grammatical meanings which are representatives of grammatical categories, they, their meanings, the categorial forms employed by the categories and the grammatical forms, that are used to express the categorial meanings are also fall into morphological study.
The units Morphology deals with are words, morphemes, forms of words, grammatical categories of words and categorial forms of words. It studies relations of these units to each other and possibilities of their use in larger units — sentences. All these units are taken both in their paradigmatic and syntagmatic aspects. The results of morphological study are classes, systems, meanings and laws of usage of these units.