Any grammatical category must be represented by at least two grammatical forms (e.g. the grammatical category of number – singular and plural forms). The relation between two grammatical forms differing in meaning and external signs is called opposition – book - books (unmarked member/marked member).
Thus grammatical oppositions expose the paradigmatic correlations of grammatical forms in a category.
All grammatical categories find their realization through oppositions, e.g. the grammatical category of number is realized through the opposition singular – plural.
The opposition may be defined as a generalised correlation of lingual forms by means of which a certain function is expressed.
The correlated elements (members) of the opposition must possess two types of features: common features and differential features. Common features serve as the basis of contrast, while differential features immediately express the function in question.
Types of opposition:
I) qualitative types