There is at least this much evidence for the reality of metaphysical knowledge. Witnesses to its existence have lived and taught since the beginning of known history, and if truthfulness and reliability have any connection with moral integrity, these witnesses have the best possible credentials. Furthermore, the witnesses to this knowledge present a much more surprising unanimity than the scientists because they have lived in such widely distant times and places that in countless instances there has been no possibility of their influencing and persuading one another.
Metaphysicians of the Christian tradition – pseudo-Dionysius, Eckhart, Albert the Great – teach essentially the same doctrine as Shankara and the Upanishads, and they in their turn the same as Chinese Taoism and the Sufis of Islam. Add to this the corroborative support of the thousands who are more strictly mystics, and we have the most impressively unanimous body of teaching in the whole world.
– Alan Watts “The Supreme Identity”