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Advaita is not the only philosophy to have reached the conclusion that 'there are not two things'. It could be argued that the essential teaching of Christ, even, is saying essentially the same ("I am that I am", "The kingdom of heaven is within you" etc.). The 'Gospel According to St. Thomas' found amongst the Dead Sea Scrolls is much less evasive and obscure than the other gospels in this respect (and is perhaps the explanation for its being kept secret at its time of writing). As was noted earlier, this was the source document for Osho's discourse 'The Mustard Seed'.
The heart of Islam is also non-dual in Sufism and Judaism has the Kabbala. Madhyamika Buddhism is non-dual, as is the Dzogchen of Tibetan Buddhism, and of course, Zen Buddhism is non-dual, too. Taoism, one of the three principal religions of China, is non-dual.
One book that compares a number of these philosophies is 'Nonduality - A Study in Comparative Philosophy' by David Loy. He is a professor at Bunkyo University Japan and is himself a Zen practitioner. The book is somewhat academically oriented, however, so will not appeal to the casual reader. There are 20 sample pages to be viewed at this Amazon link. (Buy US or UK)
"Non-dual action is spontaneous (becasue free from objectified intention), effortless (because free from a reified 'I' that must exert itself), and 'empty' (because one wholly is the action, there is not the dualistic awareness of an action)."
A sufi book recommended by Jabeen is 'The Sufi Way to Self-Unfoldment' by Shaykh F. Haeri and Fadhlalla Haeri. It is currently out of print but there may be second-hand copies available here. Excerpts may be viewed on-line here.
(Buy US or UK)
Essential Writings on Nonduality',
edited by Jerry Katz.
writings’ rather than ‘essential’ but
there is nevertheless something here to inspire
everyone and perhaps point them in a direction
to discover more about the one truth that
is the background of all appearance.
is knowledgeable in all of these
areas and weaves together the extracts well.
All disciplines are unlikely to appeal to
everyone equally. Personally, I found Ibn ‘Arabi
a revelation and Steven Harrison’s
piece on ‘Education’ excellent.
The introduction too, by David Godman, provides
a superbly concise summary of Ramana Maharshi’s
teaching. But I found Bernadette Roberts
incomprehensible and the Native American
piece overly mystical. There is a review
of the ‘Matrix’ films that is
thought-provoking and an essay by an artist
that serves to reinforce a long-standing
view that writing by artists is invariably
unintelligible – it seems that it is
because what they want to say cannot be said
that they have become artists in the first
‘Chacun à son goût’,
as they say – all of this merely reinforces
the view that there is something here for
everyone. If you are curious about what non-duality
has to offer, look no further.
for nonduality is the desire for the impossible
and the discovery of the worthwhile. The
teaching of nonduality says the worthwhile
and the impossible are not separate.
(Buy US or UK)
It is difficult to recommend specific books in areas other than Advaita since I am not myself widely read in these. (Perhaps some readers who are might like to email some recommendations, with descriptions, and I will add them to this page.)
Perhaps the most popular (and prolific) Sufi writer, whose books are generally very readable, was Idries Shah (died 1996), famous for the outwardly bumbling character, who yet acted in often very wise ways, Mulla Nasrudin. Amazon currently has 80 books by or about him, most awarded 5* rating and many having sample pages to read.
In the realm of Buddhism, I have wanted for some time to find out more about Nagarjuna, whose intellect and incisive logic were undoubtedly comaprable with those of Shankara. His key work is called the 'Mulamadhyamakakarika' and there is a highly recommended book:
'The Fundamental Wisdom of the Middle Way: Nagarjuna's Mulamadhyamakakarika' by Jay L. Garfield (Translator). The editorial description states that it 'is one of the most influential works in the history of Indian philosophy'. I almost bought this very recently but, given my financial situation and the fact that it looked as though it might require some effort on the part of the reader, I resisted the temptation. This Amazon link allows you to read 11 sample pages before buying. (Buy US or UK)
The key work in Taoism is, of course, the 'Tao Te Ching' and there are many translations and commentaries (123 results from an Amazon search). It is best to examine a few until you find a style and presentation that you like. Quite a few have sample pages for viewing at Amazon.
"Without going outside his door, one understands (all that takes place) under the sky; without looking out from his window, one sees the Tao of heaven. The farther that one goes out (from himself), the less he knows."
It is also worth looking back at Alan Watts, who has written a number of books from the standpoint of Taoism and Zen and is always readable and entertaining.