user471: I noticed some questioners on this site using the term "non-duality".
What is non-duality in Buddhism?
This is a well-known idea in Hinduism i.e. advaita. But does it exist in Buddhism?
Is it an official term in Buddhism, or just a convenient Western philosophy terminology to describe a concept just like the terms "ontology" or "epistemology"?
How is it used in Theravada and Mahayana? What are the Pali and Sanskrit terms for it?
AN 10.29 seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.

user16563: Advaita in Vedic Hinduism means Non-duality. Parallel to that "Advaya" (अद्वय) is also a Sanskrit word that means "identity, unique, not two, without a second," and typically refers to the two truths doctrine of Mahayana Buddhism, especially Madhyamaka.

Madhyamaka ("Middle way" or "Centrism"; Sanskrit: Madhyamaka, Chinese:
  中觀見; pinyin: Zhōngguān Jìan, Tibetan: dbu ma pa) also known as
  Śūnyavāda (the emptiness doctrine) and Niḥsvabhāvavāda (the no
  svabhāva doctrine) refers to a tradition of Buddhist philosophy and
  practice founded by the Indian philosopher Nāgārjuna (c. 150-250 CE).
  The foundational text of the Mādhyamaka tradition is Nāgārjuna's
  Mūlamadhyamakakārikā (Root Verses on the Middle Way). More broadly,
  Madhyamaka also refers to the ultimate nature of phenomena and the
  realization of this in meditative equipoise. Central to Madhyamaka
  philosophy is śūnyatā, "emptiness", and this refers to the central
  idea that dharmas are empty of svabhāva.

Now, Nargarjuna only explained the concept of Buddha's Nirvana in his technical words.

In the Buddhist context, nirvana refers to realization of non-self and
  emptiness, marking the end of rebirth by stilling the fires that keep
  the process of rebirth going.

Actually the word "Vaan" means to possess something(like Balvan means who is strong, Dhanvan means who is rich, Purtravan means who has sons) and "Nir" means to reject. Hence, the word Nirvana in a way means to reject all the material things and attributes including mind, body and ego which leads to Sunyata(or emptiness), similar to the concept of Advaya or Advaita, as when every enlightened soul has attained Nirvana(rejection of everthing) into emptiness, they become one in that state. It is called Brahman in Vedas and nothingless is similar to space, in which everything exists but cant be seen. Like in Vedic mathematics, numbers start from 0, similarly everything in the world manifests from 0/Shunyata/emptiness/space and ends in 0 because of death of a person/entire creation.

user254: There's a post here on that subject, which isn't long but difficult to summarise: The Dharma of Non-Duality
In the first (main) part the author says:

The word for "non-duality" is advaita
The Buddha didn't use that term (because it was already used then to mean "union of soul with God")
The Buddha did teach "non-duality" is many ways -- e.g. "neither self nor no-self", "middle way", "form and emptiness" (in the Heart Sutra), and "dependent origination implies neither self nor other"
Nagarjuna "used non-duality" in his Mulakarika
Etc.

In a second part (posted as a long comment on the first part), Hans Gruber argues that neither Nargajuna nor the Buddha teach non-duality:

Non-clinging isn't non-duality
Emptiness isn't non-duality, and different things are different even if they are dependently originated
Moving towards liberation (by reducing ignorance etc.) isn't non-duality
The Buddha didn't teach non-dualism as a metaphysical principle, instead he taught dependent origination (also didn't teach anatta as a metaphysical principle or abstract terms, but only as a "predicate" or "practice instruction" applicable to concrete terms i.e. any and all dhammas).

AN 10.29 seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.
Yes I expect it's the same root: a+dvaya ("not a pair").
Looking at advaita compared with advaya reminds me of, I wonder if it's similar to, tatha versus tathata -- where one is the adjective (e.g. "true" or "non-dual, single") and the other is an abstract noun ("truth, suchness" or "non-duality") -- or Suñña versus Suññata i.e. "empty" versus "emptiness".
That might fit with Hans Gruber's saying that the Buddha didn't non-duality as a principle (e.g. as an abstract noun).

471: <p>I noticed some questioners on this site using the term "non-duality".</p>

<p>What is non-duality in Buddhism?</p>

<p>This is a well-known idea in Hinduism i.e. advaita. But does it exist in Buddhism?</p>

<p>Is it an official term in Buddhism, or just a convenient Western philosophy terminology to describe a concept just like the terms "ontology" or "epistemology"?</p>

<p>How is it used in Theravada and Mahayana? What are the Pali and Sanskrit terms for it?</p>

<p><a href="https://suttacentral.net/an10.29/en/sujato" rel="noreferrer">AN 10.29</a> seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.</p>
 16563: <p>Advaita in Vedic Hinduism means Non-duality. Parallel to that "Advaya" (अद्वय) is also a Sanskrit word that means "identity, unique, not two, without a second," and typically refers to the two truths doctrine of Mahayana Buddhism, especially <a href="https://en.wikipedia.org/wiki/Madhyamaka" rel="nofollow noreferrer">Madhyamaka</a>.</p>

<blockquote>
  <p>Madhyamaka ("Middle way" or "Centrism"; Sanskrit: Madhyamaka, Chinese:
  中觀見; pinyin: Zhōngguān Jìan, Tibetan: dbu ma pa) also known as
  Śūnyavāda (the emptiness doctrine) and Niḥsvabhāvavāda (the no
  svabhāva doctrine) refers to a tradition of Buddhist philosophy and
  practice founded by the Indian philosopher Nāgārjuna (c. 150-250 CE).
  The foundational text of the Mādhyamaka tradition is Nāgārjuna's
  Mūlamadhyamakakārikā (Root Verses on the Middle Way). More broadly,
  Madhyamaka also refers to the ultimate nature of phenomena and the
  realization of this in meditative equipoise. <strong>Central to Madhyamaka
  philosophy is śūnyatā, "emptiness",</strong> and this refers to the central
  idea that dharmas are empty of svabhāva.</p>
</blockquote>

<p>Now, Nargarjuna only explained the concept of Buddha's <a href="https://en.wikipedia.org/wiki/Nirvana" rel="nofollow noreferrer">Nirvana</a> in his technical words.</p>

<blockquote>
  <p>In the Buddhist context, nirvana refers to realization of <strong>non-self and
  emptiness</strong>, marking the end of rebirth by stilling the fires that keep
  the process of rebirth going.</p>
</blockquote>

<p>Actually the word "Vaan" means to possess something(like Balvan means who is strong, Dhanvan means who is rich, Purtravan means who has sons) and "Nir" means to reject. Hence, the word Nirvana in a way means to reject all the material things and attributes including mind, body and ego which leads to Sunyata(or emptiness), similar to the concept of Advaya or Advaita, as when every enlightened soul has attained Nirvana(rejection of everthing) into emptiness, they become one in that state. It is called <a href="https://en.wikipedia.org/wiki/Brahman" rel="nofollow noreferrer">Brahman</a> in Vedas and nothingless is similar to space, in which everything exists but cant be seen. Like in Vedic mathematics, numbers start from 0, similarly everything in the world manifests from 0/<a href="https://en.wikipedia.org/wiki/%C5%9A%C5%ABnyat%C4%81" rel="nofollow noreferrer">Shunyata</a>/emptiness/space and ends in 0 because of death of a person/entire creation.</p>
 254: <p>There's a post here on that subject, which isn't long but difficult to summarise: <a href="https://www.christophertitmussblog.org/the-dharma-of-non-duality" rel="nofollow noreferrer">The Dharma of Non-Duality</a></p>

<p>In the first (main) part the author says:</p>

<ul>
<li>The word for "non-duality" is <em>advaita</em></li>
<li>The Buddha didn't use that term (because it was already used then to mean "union of soul with God")</li>
<li>The Buddha did teach "non-duality" is many ways -- e.g. "neither self nor no-self", "middle way", "form and emptiness" (in the Heart Sutra), and "dependent origination implies neither self nor other"</li>
<li>Nagarjuna "used non-duality" in his Mulakarika</li>
<li>Etc.</li>
</ul>

<p>In a second part (posted as a long comment on the first part), Hans Gruber argues that neither Nargajuna nor the Buddha teach non-duality:</p>

<ul>
<li>Non-clinging isn't non-duality</li>
<li>Emptiness isn't non-duality, and different things are different even if they are dependently originated</li>
<li>Moving towards liberation (by reducing ignorance etc.) isn't non-duality</li>
<li>The Buddha didn't teach non-dualism as a metaphysical principle, instead he taught dependent origination (also didn't teach anatta as a metaphysical principle or abstract terms, but only as a "predicate" or "practice instruction" applicable to concrete terms i.e. any and all dhammas).</li>
</ul>

<p><strong>AN 10.29 seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.</strong></p>

<p>Yes I expect it's the same root: a+dvaya ("not a pair").</p>

<p>Looking at <em>advaita</em> compared with <em>advaya</em> reminds me of, I wonder if it's similar to, <a href="https://dsalsrv04.uchicago.edu/cgi-bin/app/pali_query.py?qs=Tatha&amp;searchhws=yes" rel="nofollow noreferrer">tatha versus tathata</a> -- where one is the adjective (e.g. "true" or "non-dual, single") and the other is an abstract noun ("truth, suchness" or "non-duality") -- or <a href="https://dsalsrv04.uchicago.edu/cgi-bin/app/pali_query.py?qs=Sunna&amp;searchhws=yes" rel="nofollow noreferrer">Suñña versus Suññata</a> i.e. "empty" versus "emptiness".</p>

<p>That might fit with Hans Gruber's saying that the Buddha didn't non-duality as a principle (e.g. as an abstract noun).</p>
