This talk presents an overview of the development of a model of phonotactic grammar in which well-formedness of consonant clusters is measured by NAD (Dziubalska-Kołaczyk 2014, 2019). NAD stands for a Net Auditory Distance obtaining between segments in a cluster. The auditory distance is a net reflection of the differences between segments in terms of manner (MOA) and place of articulation (POA). It is calculated according to the Principle which states that a cluster is preferred if it satisfies a pattern of distances specified by the universal phonotactic preference relevant for its position in a word. Every position of a cluster in a word, i.e. initial, medial and final, is defined by a respective well-formedness (“goodness of cluster”) preference. The NAD Principle makes finer predictions than the sonority sequencing principle (Clements 1990, Selkirk 1984). For example, it predicts that initial pr- is “better” (more preferred) that tr-, and they are both better than ps- or rt-, while the latter two are of comparable value.

However, phonology alone does not fully account for clusters. Inflection, word-formation and compounding contribute to the creation of consonant clusters to an extent relative to a morphological type of a language. Therefore, a phonotactic grammar operates on basic, non-derived, lexical forms, while morphonotactics (Dressler and Dziubalska-Kołaczyk 2006) takes care of the remaining, morpho- logically complex, forms. Interaction between phonotactics and morphonotactics provides a richer insight into the understanding of cluster complexity.