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.