The focus of this chapter is on the appropriate tools for the analysis of tonal phonology. Before we study the behaviour of tone in any detail, we need a common framework in which to couch our analyses. In section 4.1, I will begin by identifying five properties of tone that any analytical framework must be able to capture. Section 4.2 shows that an ‘autosegmental’ representation nicely deals with these properties. Section 4.3 introduces the Optimality Theory framework, and section 4.4 extends it to tonology. Section 4.5 applies the framework to the five central properties of tone, and sections 4.6–10 flesh out a full working model of tonal phonology within Optimality Theory.

Tone differs from many other phonological features in the following ways, rarely or never observed in more familiar consonantal or vocalic features:

1. a. Mobility: Movement away from point of origin

2. b. Stability: Survival after loss of original host segment

3. c. One-to-many: A single tonal feature shared by two or more segments

4. d. Many-to-one: Multiple tonal features surfacing on a single host segment

5. e. Toneless segments: Potentially tone-bearing segments that never acquire phonological tone

The only non-tonal features that regularly exhibit any of these characteristics are harmonizing features like nasality and certain vowel features, which may spread over large domains from their source segments. Features like consonantal place features, or laryngeal features like aspiration and voice, do not usually show these behaviours.