This book has been about the contrastive hierarchy in phonology. In one sense, ‘phonology’ refers to phonological theory as it has been understood and practised from the 1920s until today. I have tried to trace the history of the notion of a contrastive feature hierarchy, and its various guises as it has appeared and disappeared in different versions of phonological theory. In another sense, ‘phonology’ can be understood as a component of the language faculty whose properties phonologists are trying to discover. In this sense, I have looked for evidence of the role that the contrastive hierarchy plays in contributing to an understanding of this cognitive domain.

In both aspects of this study the fate of the contrastive hierarchy has been closely connected to another central concept, the Contrastivist Hypothesis. The Contrastivist Hypothesis states that only contrastive features are active in the phonology. To properly test whether this hypothesis is correct, we need to have reliable ways of identifying the ‘contrastive features’. We also need to know what it means for a feature to be ‘active’, and what place ‘in the phonology’ refers to; but my main concern here has been contrast. I have argued that the contrastive hierarchy is crucial to the Contrastivist Hypothesis, because it provides the proper way to identify contrastive features. Conversely, the Contrastivist Hypothesis is crucial to the contrastive hierarchy, because the former supplies the main empirical reasons for being interested in the latter, at least as far as phonology is concerned.