Concept A is a generalization of concept B if and only if:
- every instance of concept B is also an instance of concept A; and
- there are instances of concept A which are not instances of concept B.
Equivalently, A is a generalization of B if B is a specialization of A.
This kind of generalization versus specialization (or particularization) is reflected in either of the contrasting words of the word pair hypernym and hyponym. A hypernym as a generic stands for a class or group of equally-ranked items, such as tree does for beech and oak; or ship for cruiser and steamer. Whereas a hyponym is one of the items included in the generic, such as lily and daisy are included in flower, and bird and fish in animal. A hypernym is superordinate to a hyponym, and a hyponym is subordinate to hypernym.