Humans use language to communicate. They utter certain sounds and respond to others uttering sounds in ways that constitute communication. What exactly is going on? How is this possible? We all know that it is because the expressions of a language are meaningful that we can use them for communication. Philosophers of language try to expand on this tautological and uninformative answer by constructing a more detailed theory of meaning. Such a theory may answer questions such as 'What is it for an utterance to be meaningful?', 'Why does a particular sound have the meaning it has?', 'How do people know what an utterance means?' and so on. By answering such questions, and by introducing new concepts and principles governing these concepts as well as linking them with other, familiar concepts, a theory of meaning will provide a more detailed explanation of what is going on when humans use language to communicate.