Languages organize their parts of speech into classes according to their functions and positions relative to other parts. All languages, for instance, make a basic distinction between a group of words that prototypically denotes things and concepts and a group of words that prototypically denotes actions and events. The first group, which includes English words such as dog and song, are usually called nouns. The second, which includes think and sing, are called verbs. Another common category is the adjective: words that describe properties or qualities of nouns, such as red or big. Word classes can be open if new words can continuously be added to the class, or relatively closed if there is a fixed number of words in a class. In English, the class of pronouns is closed, whereas the class of adjectives is open, since an infinite number of adjectives can be constructed from verbs (e.g. saddened) or nouns (e.g. with the -like suffix, as in noun-like). In other languages such as Korean, the situation is the opposite, and new pronouns can be constructed, whereas the number of adjectives is fixed.