Set and classification, word classes, the verb

A collection of various objects, events or phenomena taken for study is called a set. For example, all the school supplies in a classroom form one set. Dividing a set into inner groups on the basis of similar and different features is classification. Fruits, for instance, can be grouped by colour, ripening time or place of growth. For classification we first choose a feature (basis), then group everything by it. In linguistics too the set of words is classified: words are divided into word classes by their question and meaning.