1. Assagioli, R. (1965). Psychosynthesis. Penguin Books.
2. Batthyány, A. (2010). Viktor E. Frankl and the development of logotherapy & existential analysis [Introduction]. In The feeling of meaninglessness (pp. 7–39). Marquette University Press.
3. Blavatsky, H. P. (1888). The secret doctrine, Volume I: Cosmogenesis (Vol. 1, 3rd ed.). Theosophical Publishing Society.
4. de Mello, A. (1982/1984). The song of the bird. Image Books.
5. DuBois, J. M. (2004). Understanding Viktor Frankl’s Theory and Therapy of Mental Disorders [Editor’s Introduction] (J. DuBois, Trans.). In On the theory and therapy of mental disorders: An introduction to logotherapy and existential analysis (pp. ix–xliii). Brunner-Routledge.