One of the first things that people noticed when they started thinking about language as language was that words tend to fall into categories and that the members of these categories behave in similar ways. The traditional name for those categories is the "parts of speech." In this chapter, we will look at these word categories and see how the traditional account is somewhat misleading, as well as inaccurate. With a more accurate idea of word categories, we will be equipped with the basics that we need to begin studying sentence structure.