As we've seen, words allow people to refer to a potentially very large number of things in the world, either directly with proper nouns, or indirectly through semantic categories of utterance roles (such as hearer) with common nouns and personal pronouns. But even the flexibility that comes with common nouns is limited. No matter how many categories a speech community labels with nouns, there will always be multiple members of particular categories that need to be distinguished from each other, for example, one apple from another. Coming up with new categories and new labels for them is a slow process, certainly not fast enough to cope with the minute-to-minute demands of communication, where the difference between one apple and another may matter a lot. This chapter is about the way people cope with this need by making use of one of the most fundamental properties of human language, compositionality, the power to combine words into phrases whose meanings are combinations of the meanings of the words. The focus is on noun modification, the use of words in combination with nouns to restrict the meanings of the nouns. In later chapters, we will see how compositionality allows us to refer to events and states as well as things.