Shankaracarya's Upadesa Sahasri/ A Thousand Teachings a work that is regarded as authentic and unique for him because it is not a commentary on any part of the triple canon i.e. Bhagavad Gita, Brahma Sutras or Upanishads; presents in its first chapter A Method of Enlightening the Disciple. (All quotations are from the translation by Swami Jagadananda published by Sri Ramakrishna Math, Chennai) Text at:
A Thousand Teachings
Both to give and to receive instruction require preconditions. On the side of the pupil who is typically taken to be
a pure Brahmana disciple who is indifferent to everything that is transitory and achievable through certain means, who has given up the desire for a son, for wealth and for this world and the next, who has adopted the life of a wandering monk and is endowed with control over the mind and senses, with compassion etc.,
The central requirement is "self-control and a tranquil mind" which is not gender or caste specific. Clearly knowledge of this kind is not simply a matter of the transmission of information. Distortions will occur if the moral base is not established.
When the teacher finds from signs that knowledge has not been grasped (or has been wrongly grasped) by the disciple, he should remove the causes of non-comprehension which are past and present sins, laxity, want of previous firm knowledge of what constitutes the subjects of discrimination between the eternal and the non-eternal, courting popular esteem, vanity of caste etc., and so on, (he should remove) through means contrary to those causes, enjoined by the Srutis and Smrtis viz. avoidance of anger etc., and the vows (Yama) consisting of non-injury etc., also the rules of conduct that are inconsistent with knowledge.
The great teachers who are liberated themselves, the sat-gurus, can nullify the occluding factors and bring a glimpse of the truth even to the unworthy. Simply to be in their presence is enough. Other teachers not quite at that level must have
the power of furnishing arguments pro and con, of understanding questions and remembering them, who possesses tranquillity, self-control, compassion and a desire to help others, who is versed in the scriptures and unattached to enjoyments both seen and unseen, who has renounced the means to all kinds of actions, is a knower of Brahman and established in It, is never a transgressor of the rules of conduct , and who is devoid of shortcomings such as ostentation, pride, deceit, cunning, jugglery, jealousy, falsehood, egotism and attachment.
In the traditional way there is an order of business once the moral bases of both teacher and pupil are well founded. The scriptural texts which summarise the highest teaching are sown like seeds on well plowed and harrowed ground. "All this is but the Self", "All this is verily Brahman". The definition of Brahman comes next - "It is the seer Itself unseen", "Existence, Knowledge, Infinite". The texts from the scriptures on this topic are multitudinous.
This is the traditional foundation for a rational inquiry. Of that more anon.