Is “ai” a Unitary or Separate Morpheme?

Yorubá is one of the major languages spoken in Nigeria alongside Hausa and Igbo. It has enjoyed extensive research works from both native and non-native authors in virtually all the sub-fields of linguistics. However, there are areas of disagreement among scholars, one of which is the status of the negative maker "ai" as a morpheme or two morphemes. This argument, among other reasons, prompted this paper. Albeit, Oye (2007) argues that negative marker /ai/ is a morpheme while Awobuluyi (2005), Adewole (1992) Solomon (1983) and Olumuyiwa (2006) have a contrary opinion, they claim that the negative prefix marker /ai/ is two morphemes. In this paper, we shall examine the arguments of Yoruba scholars on the negative prefix marker /ai/ as to whether it a unitary morpheme or two separate morphemes. We shall argue in this paper, that the morpheme /i/ has two variants; one is a nominal prefix while the other is a negative marker and the variants are in complementary distribution. We shall also show in this paper that /a/ is a nominal prefix while /i/ is the negative marker in support of the earlier scholars that claim that /ai/ is two morphemes.