Morphology is at the conceptual centre of linguistics. This is not because it is the dominant subdiscipline, but because morphology is the study of word structure, and words are at the interface between phonology, syntax and semantics. Words have phonological properties, they articulate together to form phrases and sentences, their form often reflects their syntactic function, and their parts are often composed of meaningful smaller pieces. In addition, words contract relationships with each other by virtue of their form; that is, they form paradigms and lexical groupings. For this reason, morphology is something all linguists have to know about. The centrality of the word brings with it two important challenges. First, there is the question of what governs morphological form: how is allomorphy to be described? The second is the question of what governs the syntactic and semantic function of morphological units, and how these interact with syntax and semantics proper.