Feature economy is a principle of sound systems according to which languages tend to maximise the ratio of sounds over features. The major goal of this study is to confirm the predictions of feature economy at the synchronic level, using an objective sampling technique applied to a genetically and areally balanced sample of the world's languages. It also shows that feature economy can be used as a tool in phonological feature analysis, and offers voiced aspirates, voiceless sonorants and various types of glottalised sounds as illustrations. Feature economy applies not only to distinctive feature values, but to redundant values of features that are distinctive or phonologically active elsewhere in the system. Feature economy cannot be reduced to a purely phonetic principle of gesture economy, but may reflect a general principle of linguistic organisation according to which the active categories of a grammatical system tend to be used to maximal effect.

This paper presents evidence that tongue-body position is always specified in the phonological representation of coronals, even where it is non-contrastive. Tongue-body position is needed to account for the typology of interactions between coronal consonants and adjacent vowels. For example, coronals only condition vowel fronting if they are produced with a front tongue body (usually anterior coronals), and only coronals produced with a back tongue body (usually retroflexes) condition vowel retraction. However, coronals do not have a fixed tongue-body position. Tongue-body position is affected by the position of the tongue tip/blade, because these articulators are physically connected, so each type of coronal has a preferred tongue-body position that facilitates the production of the coronal constriction. These preferences can be overridden, however, e.g. due to assimilation to a vowel. Optimality-theoretic feature co-occurrence constraints provide a good account of this type of dependency between articulators.

In nasal harmony systems, any major consonant class (excluding laryngeal glides) may fail to undergo nasalisation. This paper proposes to derive the neutrality of stops, fricatives, liquids and glides from the satisfaction of a special set of faithfulness constraints; each member of the set commands the presence of a particular segment class in a consonant inventory. The analysis requires that the constraint commanding the presence of stops be active in every grammar and invariably take precedence over the demands of nasal harmony. The explanation of stop neutrality forces a rethinking of the nature of constraints and how they interact. The paper argues that the constraints regulating the cross-linguistic manifestation of segment neutrality are either universal grammatical features (i.e. principles) or language-specific choices (i.e. parameters of variation). It also postulates that constraint interaction is regulated by a set of metaconditions that determine ordering; constraint ranking is not random.