1. Abraham, W. (1962). The mind of Africa. Chicago: University of Chicago Press.
2. Austin, A. L. (1962). How to do things with words. Cambridge: Harvard University Press.
3. Ayer, A. J. (1936). Language, truth and logic. London: Gollancz.
4. Ayer, A. (1946). Language truth and logic. New York: Dover Publications.
5. Barry Hallen. 2001. The good, the bad and the beautiful. Discourse about Values in Yoruba Culture. Bloomington: Indiana University Press.