Dialects

The Yoruba dialect continuum itself consists of various dialects. The various Yoruba dialects in the Yorubaland of Nigeria can be classified into three major dialect areas: Northwest, Central, and Southeast.^[7] Of course, clear boundaries can never be drawn and peripheral areas of dialectal regions often have some similarities to adjoining dialects.

North-West Yoruba is historically a part of the Ọyọ empire. In NWY dialects, Proto-Yoruba /gh/ (the velar fricative [ɣ]) and /gw/ have merged into /w/; the upper vowels /i ̣/ and /ụ/ were raised and merged with /i/ and /u/, just as their nasal counterparts, resulting in a vowel system with seven oral and three nasal vowels. Ethnographically, traditional government is based on a division of power between civil and war chiefs; lineage and descent are unilinealagnatic.

South-East Yoruba was probably associated with the expansion of the Benin Empire after c. 1450 AD.^[8] In contrast to NWY, lineage and descent are largely multilineal and cognatic, and the division of titles into war and civil is unknown. Linguistically, SEY has retained the /gh/ and /gw/ contrast, while it has lowered the nasal vowels /ịn/ and /ụn/ to /ẹn/ and /ọn/, respectively. SEY has collapsed the second and third person plural pronominal forms; thus, àn án wá can mean either 'you (pl.) came' or 'they came' in SEY dialects, whereas NWY for example has ẹ wá 'you (pl.) came' and wọ́n wá 'they came', respectively. The emergence of a plural of respect may have prevented coalescence of the two in NWY dialects.

Central Yoruba forms a transitional area in that the lexicon has much in common with NWY, whereas it shares many ethnographical features with SEY. Its vowel system is the least innovating (most stable) of the three dialect groups, having retained nine oral-vowel contrasts and six or seven nasal vowels, and an extensive vowel harmony system.

Standard Yoruba (also known as literary Yoruba, the Yoruba koiné, common Yoruba and often simply as Yoruba) is a separate member of the dialect cluster. It is the written form of the language, the standard variety learnt at school and that spoken by newsreaders on the radio. Standard Yoruba has its origin in the 1850s, when Samuel A. Crowther, native Yoruba and the first African Bishop, published a Yoruba grammar and started his translation of the Bible. Though for a large part based on the Ọyọ and Ibadan dialects, Standard Yoruba incorporates several features from other dialects^[9]. Additionally, it has some features peculiar to itself only, for example the simplified vowel harmony system, as well as foreign structures, such as calques from English which originated in early translations of religious works.

Because the use of Standard Yoruba did not result from some deliberate linguistic policy, much controversy exists as to what constitutes 'genuine Yoruba', with some writers holding the opinion that the Ọyọ dialect is the most "pure" form, and others stating that there is no such thing as genuine Yoruba at all. Standard Yoruba, the variety learnt at school and used in the media, has nonetheless been a powerful consolidating factor in the emergence of a common Yoruba identity.