All four methods described in chapter five (phenomenological, inductive-deductive, transpersonal and reasoning) can contribute to this subject, but each of them is understandably somewhat limited, so combining them is essential in this case:
Relevant materials from various traditions (the Tibetan Book of Death arguably still being the most authoritative one). Phenomenological method can help in separating the essence from its cultural embodiments. Discerning commonalities from different backgrounds may also be facilitative, although they could stem from cross-cultural fertilisation, rather than genuine similarities in experience.
Research on Near Death Experiences (NDE). This source, however, can account only for the first stages of life after death and relies on untrained subjects (although some aspects of their reports can be verified).
Transpersonal insights are essential, but they can be easily misinterpreted (e.g. they may relate to something else, rather than life after death).
Reasoning is limited in its generating role, although some deductive inferences can be drawn to make an account complete. This method can also exclude elements that are inconsistent, incongruent with the available facts, and superfluous.
- . For instance, in Ancient Greece, Empedocles and Plato adopted the idea of reincarnation from the Pythagoreans, and Pythagoras himself had probably learned of it from his contacts with India.