Known as the ten undeclared topics, these are the statements that Gotama, the Buddha, refused to give a view on:
- the world is eternal
- the world is not eternal
- the world is finite
- the world is infinite
- the soul is the same as the body
- the soul is one thing and the body another
- after death a tathagata exists
- after death a tathagata does not exist
- after death a tathagata both exists and does not exist
- after death a tathagata neither exists nor does not exist.
The context of the questions that Gotama refuses to answer suggests that he is addressing the large imponderable questions that trouble all human beings at some point in their lives, not specific issues of Buddhist theology.
While they are found in many suttas, it may be useful to look first at Cūḷamālunkya Sutta. M. 63, and Udāna, 6.4-6. Note that while the Buddha refused to be drawn on these topics, he did say that what he did ‘declare’ were the four noble truths, (calling them perhaps the four great tasks or the fourfold task would express this better).
For a number of reasons, I find the four last topics (regarding a tathāgata after death) as fishy. My sense is that these were incorporated later to replace the more problematic (for traditional Indian Buddhists): ‘The self exists after death; the self does not exist after death.’ Not only would such a formulation be more in keeping with the other topics, it would also be the sort of thing discussed by ‘brahmins and ascetics’ who were not Buddhist, as is indeed the case with the Udana passages mentioned above.