These words refer to groupings of similar things. Kind can indicate a grouping that has indisputable objective reality: a poker hand that contained four of a kind . More informally, it can also indicate a subjective notion on the part of a speaker that two or more things are alike in some way: I don’t like people of that kind ; the kind of room that I can feel at home in. often the word can be used when no very serious reference to a larger grouping is actually intended: He was a friendly kind of person. Sort is even more informal than kind . Occasionally, it can refer to clearly defined groupings that are objectively valid: a list of the sorts of tree that are hardy enough to grow in cities, despite the hazard of air pollution. But even more often than kind , the word suggests a subjective evaluation. Furthermore, the word more often indicates a negative judgement: the wrong sort of person for her son to be associating with.

Type is only slightly more formal than the foregoing, but it points more clearly to objectively definable groupings: the four basic types of blood; types of world literature. But it can be used in the same indefinite way as kind and sort , although it may carry over a note of greater conviction: What an ugly type of building. A special use of the word refers to an individual or example as though it were the quintessence of a whole group: He was an Air Force type ; a beatnik type . Some careful writers avoid this informal usage – or any use of the preceding words that suggests the existence of hard-and-fast classifications where this is not the case. Category , the most formal of these words, applies exclusively to definable grouping, whether they are arbitrarily developed for the sake of order or convenience: self-evident categories based on the results of a single chemical test; She made categories of the things she wanted to take with her, things she wanted put into storage, and things to be discarded.