Daniels, M.D., D.; Price, PhD, V., The Essential Enneagram, New York: HarperCollins, 2000
延伸閱讀
Ronald Knox. Enthusiasm: a Chapter in the History of Religion, with Special Reference to the XVII and XVIII Centuries. Oxford, Eng.: Oxford University Press, 1950. viii, 622 p.
John Locke. An Essay Concerning Human Understanding. vol. 2. New York: Dover Publications
Susie Tucker. Enthusiasm: A Study in Semantic Change. London: Cambridge University Press