The relation between morphology and phonology is an intimate one, both synchronically and diachronically. Thus, for example, allomorphic variation of affixes is frequently determined by phonological context, and affixation itself often imposes phonological requirements. There are also non-affixal morphological relations, such as umlaut, whose origins are purely phonological. Thus linguistic phenomena which belong to one domain at one time, may belong to the other at a later time. The traditional approach to such phenomena is to maintain a distinction between two levels of description, with morphosyntactic features triggering morphological processes, such as affixation, and with phonological processes following. In recent years, however, NLP-researchers working on phonology and morphology have tended to adopt declarative, constraint-based approaches, and it is such an approach that we presuppose throughout this tutorial. Although we will make a distinction between phonological structure and morphotactics, and between attributes in the phonological domain and those in the morphological domain, we do not encourage you to embrace the traditional notion of level of description, nor its concomitant notion of rule type (or process) mapping from one level to another. The linguistic description is just a set of simultaneously applicable constraints. Such constraints may, for example, directly connect morphosyntactic attributes to individual phonological components of word forms. The explicit definition of elements of the phonological structure by reference to morphosyntactic features is fundamental, and is described in more detail in the phonology sections.
