1. Barbour, J. (1974). Myths, models and paradigms: The nature of religious and scientific language. New York: Harper & Row.
2. 5-D or 1?
3. den Draak, C. (1989). Bidden en Gebedstaal: Psychologische studie naar aanleiding van onderzoek onder jongeren [Praying and prayer-language: A psychological study on the basis of a survey among youth]. Unpublished master's thesis, University of Nijmegen, The Netherlands.