One interesting question in vowel systems is how many distinctions of vowel height (or aperture) are made in a language. The most typical vowel system in the world’s languages has five vowels and three degrees of height (i, e, a, o, u) (Maddieson 1984: 126), but systems with four degrees (i, e, ɛ, a, ɔ, o, u) are not uncommon either, and even five degrees (i, ɪ, e, ɛ, a, ɔ, o, ʊ, u) are possible.
For this chapter, we only took major allophones and non-nasal vowels into account, regardless of length distinctions, and we ignored the central vowel [ə] (schwa), whose height properties are difficult to determine. We treated [a], [æ] and [ɑ] as having the same height. Most vowel systems are symmetrical, but when a system has four heights in the front range and three heights in the back range, for example, it is counted as having four heights.
|Two vowel heights||3|
|Three vowel heights||31|
|Four vowel heights||36|
|Five vowel heights||6|
The map shows both a lexifier effect and a geographical effect: Languages whose lexicon is based on English, Dutch, French, and Portuguese show a clear tendency to have four or even five vowel heights (like the lexifier), while the other languages show a clear tendency to have three or even just two vowel heights.
In geographical terms, languages of the Atlantic region tend to have four vowel heights, while languages of the Asia-Pacific region tend to have fewer vowel heights.
There are exceptions to these generalizations; in particular, the Atlantic region has three Portuguese-based languages with three heights (Casamancese Creole, Guinea-Bissau Kriyol, Fa d’Ambô), and six English-based languages with three heights (Nengee, (Early) Sranan, Trinidad English Creole, Nicaraguan and San Andres Creole English). But the languages outside this region with a four-level system are all Portuguese-, French- or English-based. And the only French-based language with a three-level system is Tayo (in the Pacific). There are three English-based languages in the Pacific region with a three-level system (Tok Pisin, Bislama, Kriol), and one Portuguese-based language (Batavia Creole).
In the Atlantic region, there are two Spanish-based languages (Palenquero and Papiamentu) and one African language (Sango) with a four-level system. Parkvall (2000: 25-27) discusses possible substrate influences from West African languages on Atlantic creoles, and Klein (2006) notes that creole vowel systems show no tendency to be particularly small.