In chapter 1 we noted that morphology (the study of word structures) and syntax (the study of phrase and sentence structures) are generally treated as separate sub-fields in linguistics. This is because words and sentences are different in certain fundamental ways. After studying chapter 2 you have some idea of how we might represent the arrangement of morphemes in a word, at least in the simplest cases. Describing the arrangement of words in a sentence will require some additional concepts.

In this chapter we discuss two fundamental aspects of sentence structure. First, the words of any language can be classified according to their grammatical properties. These classes are traditionally referred to as parts of speech (noun, verb, etc.); linguists refer to them as syntactic categories. In describing the word-order patterns of the language, we need to refer to syntactic categories since it is obviously impossible to list every possible combination of specific words.

Second, the words in a sentence are not organized as a simple list. Rather, words cluster together to form groups of various sizes; these groups are referred to as constituents. The word-order patterns of human languages cannot be described adequately without reference to constituents.

In this chapter we will discuss the kinds of linguistic evidence we can use to identify constituents (groups of words) and categories (parts of speech). Then we will discuss “tree” diagrams, a commonly used method for representing both the grouping of words and the linear order of words in a sentence.