The opposition may be defined as a generalized 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.
Three main qualitative types of oppositions were established in phonology: privative, gradual, and equipollent. By the number of members contrasted, oppositions were divided into binary and more than binary (ternary, quaternary, etc.).
The most important type of opposition in morphology is the binary privative opposition.
Equipollent oppositions in the system of English morphology constitute a minor type and are mostly confined to formal relations only.
Gradual oppositions in morphology are not generally recognized. They can be identified as a minor type at the semantic level only.
Members of morphological oppositions unlike those of phonological oppositions possess both the plane of expression and the plane of content.