1. Clayton, V.P. & Birren, J.E. (1980). The development of wisdom across the life span. In P.B. Baltes & O.G. Brim Jr. (Eds.), Life Span Development and Behavior, Vol. 3 (pp. 103-135). New York: Academic Press.
2. Digeser, P.E. (2001). Political forgiveness. Ithaca: Cornell University Press.
3. Donadio, S., Smith, S., Mesner, S. & Davison, R. (1992). The New York public library book of 20th century American quotations. New York: Warner Books.
4. Erikson, E. (1997). The life cycle completed. Extended version by J.M. Erikson. New York: Norton.
5. Hadot, P. (1995). Philosophy as a way of life. Malden, MA: Blackwell Publishing.