Sonority hierarchy

A sonority hierarchy or sonority scale is a ranking of speech sounds (or phones) by amplitude. For example, if one says the vowel [a], they will produce a much louder sound than if one says the stop [t]. Sonority hierarchies are especially important when analyzing syllable structure; rules about what segments may appear in onsets or codas together, such as SSP, are formulated in terms of the difference of their sonority values. Some languages also have assimilation rules based on sonority hierarchy, for example, the Finnish potential mood, in which a less sonorous segment changes to copy a more sonorous adjacent segment (e.g. -tne- → -nne-).

Sonority hierarchies vary somewhat in which sounds are grouped together. The one below is fairly typical:

Sound types are the most sonorous on the left side of the scale, and become progressively less sonorous towards the right (e.g., fricatives are less sonorous than nasals).

The labels on the left refer to distinctive features, and categories of sounds can be grouped together according to whether they share a feature. For instance, as shown in the sonority hierarchy above, vowels are considered [+syllabic], whereas all consonants (including stops, affricates, fricatives, etc.) are considered [−syllabic]. All sound categories falling under [+sonorant] are sonorants, whereas those falling under [−sonorant] are obstruents. In this way, any contiguous set of sound types may be grouped together on the basis of no more than two features (for instance, glides, liquids, and nasals are [−syllabic, +sonorant]).

least sonorous (strongest consonantality)

In English, the sonority scale, from highest to lowest, is the following:

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