Who first used the term nididhysana? Shankaracharya or Ramana Maharshi?
Is nididhyasana meditation or mere contemplation?
If its meditation, then how is it different from Patanjali's meditation techniques?
If its contemplation, then how does constant deep thinking gives a person moksha from cycle of rebirth?
If its reminding oneself that he is Brahman, by repeating the mahavakyas, then can such reminders and repetition of mahavakyas bring moksha from cycle of rebirth?
You have many questions few among which are answered as follows:
Nididhyasana is a scriptural term. So neither Adi Shankara nor Ramana Maharshi was the first person to use it. The term can be found in Puranas.
From Devi Bhagavtam 7.34:
...... then works become beneficial and helping to Jñânam. (Therefore the Jîvas should take up both of these.) Others say that this is impossible owing to their contradictory natures. The knots of heart are let loose by Jñânam and the knots are knit more by Karma. So how can they be reconciled? They are so very diametrically opposite. Darkness and light cannot be brought together, so Jñânam and Karma cannot be brought together. Therefore one ought to do all the Karmas as best as one can, as enjoined in the Vedas, until one gets Chittas'uddhi (the purification of one's heart and mind). Karmas are to be done until S'ama (the control of the inner organs of senses), Dama (the control of the outer organs of senses), Titiksâ (the power to endure heat and cold and other dualities), Vairâgyam (Dispassion), Sattva Sambhava (the birth of pure Sattva Guna in one's own heart) take place. After these, the Karmas cease for that man.
Then one ought to take Sannyâsa from a Guru (Spiritual Teacher) who has got his senses under control, who is versed in the S'rutis, attached to Brahma (practising the Yogic union with Brahma). He should approach to him with an unfeigned Bhakti. He should day and night, without any laziness, do S'ravanam, Mananam, and Nididhyâsanam (hearing, thinking and deeply realising) the Vedânta sayings. He should constantly ponder over the meanings of the Mahâvâkyam "Tat Tyam Asi." "Tat Tyam Asi" means Thou art That; it asserts the identity of the Supreme Self (Brahma) and Embodied Self (Jîvâtmâ). When this identity is realised, fearlessness comes and he then gets My nature.
Another instance where it is found in Puranas is in Shiva Gita:
13.4. Means for rise of Knowledge.
Rāma wanted to be enlightened on how does sacred knowledge about Śiva arise in a mortal and means in that matter. Lord, further, explains the way to acquire the purest knowledge, by his grace, to the great Rāma. Abandoning all attachment to entire creation, including ones own kith and kin, and having faith in the scriptures and longing for vedantic wisdom, with gifts in hand one should approach a learned and realized preceptor and please him with services and hear with intense concentration (śravaṇa) about the essence of Upaniṣads in the form of Mahāvākyas and reflect (manana) on them and do constant contemplation (nididhyāsana) on oneself Abhijñāna Śākuntala the Supreme Self and by grace of god, all past karmas gets burnt in the fire of knowledge and the devotee do not acquire any subsequent karmas and becomes a realized one; a Brahma-Jñāni becomes himself Brahman. After realization one happens to incur whatever sin, does whatever meritorious deeds, great or small, he is not affected by such sin or merit. Such a person is Jīvan-mukta. When all the desires in a person are controlled and conquered, then the mortal turns into immortal.[4] Release is known Abhijñāna Śākuntala the destruction of the knots of heart caused by ignorance.
According to Vedanta Sarah of Sri Sadanandayogindrasaraswati, the Sadhana of an Advaitin comprises of the following (he has given a flow chart at the end of the book):
- One must forsake Nishiddha Karmas (acts forbidden by scriptures) and Kamya Karmas (acts that are performed with certain goals in mind).
- With due performance of Nitya Karmas (obligatory acts like Sandhyavandanam etc) and Naimittik Karmas (occasional rites), Prayaschittas (penances), the aspirant needs to attain Chittasuddhi (purification of mind) and Mumukshtatva (a desire for Moksha).
- Guropodesha (Initiation of Guru's teaching)
- Shravana (Hearing the Mahavakyas and Guru's teachings). Understanding their meanings using a six fold method (Upakrama, Upasamhara, Abhyasa etc.).
- Manana (contemplating and realizing the meaning through arguments).
- Nididhyasana
7.Samadhi
The definition of Nididhyasana that is given in the book is mentioned in verse 192 and is as follows:
vijAtiya-dehAdi-pratyaya-rahita-advitiyavastu-sajatiya pratyaya-pravAhah nididhyAsanam || 192
Depriving the mind from any external thoughts of Brahman (like body etc.), when mind and thoughts are focused on only the Adavitic nature of Brahman is called Nididhyasana.
Amrita commentary on this verse is as follows:
Nididhyasana is uninterrupted Dhyana (meditation). No other thought processes (Chitta Vritti) must arise in it. After Shravana (hearing) and Manana (contemplation of what has been heard), the mind gets fixated into one form (Swarupa) and when no other forms arise in the mind other than that Swarupa, that is called Nididhyasana. By continuous discrimination through "Neti Neti" (not that, not that method) what remains is the Consciousness (Chaitanya) and to fix the mind only on that Consciousness is called Nididhyasana.
According to Advaita, by performing Nididhyasana, the aspirant attains Samadhi (which can either be Nirvikalpa or Savikalpa) and which results in self realization.
EDIT:
I have found an English copy of the Vedanta Sarah book that I have used in this answer here.
The definition of Nididhyasana is found on page 83 of the PDF.
In my case the book is in Sanskrit-Bengali and here the book is in Sanskrit-English. Also the translators are different.
Answering Q1
Nididhyasanam is an upanishadic term , (may occur in prakarana granthas(texts) but isn't coined in them.)
Saadhana Chatustaya(SC) sampathi advocated by HH Adi shankara is the precursor for Shravana Manana Nidhidhyasanam(SMN) .
It is futile to embark on SMN without self-introspecting on own SC sampathi,( If one can't achieve SC, Bhagavad Gita suggests Karma Yoga.)
Yamaha and Niyamaa are supposed to be the stepping stone for yoga path.
From what I know, shravana is getting to know of (listen) from vedantic scriptures , (so here the listener is never misinformed), Mananam is feasibility study that removes doubts , Nidhidhyasanam is turning it into experiential reality.
But Nidhidhyasanam on mahavakyas (not an object of any knowledge) is far-fetched and tougher than any upaasana .
Brihadaranyaka Upanishad (2.4.5) आत्मा वा अरे द्रष्टव्यः श्रोतव्यो मन्तव्यो निदिध्यासितव्यो मैत्रेयि,आत्मनो व अरे दर्शनेन श्रवणेन मत्या विज्ञानेनेदं सर्वं विदितम् ||" Ãtmã vã are drashtavyaha shrotavyo mantavyo nididhyãsitavyaha...(sage yagnyavalkya) The Self, my dear Maitreyi, should be realized – should be heard of, reflected on and medtated upon;by the realization of the Self, my dear, through hearing, reflection and meditation, all this is known."
Panchadhashi (Praakarana grantha, Swami vidhyaranya) chapter 1 verse 54 ittha.n vaakyais tad arthaanusandhaana.n shravaNaM bhavet.h .yuktyaa sambhaavitatvaanusandhaanaM manana.n tu tat.h .. When the ideas that we have gathered through hearing and studying from a preceptor are made to enter our feelings by deep reflection on the same, and when these ideas that have become practically part of our nature by way of deep investigation—when concentration and reflection become inseparable from us—we become absorbed in them to such an extent that we think only these ideas. Our very outlook changes in terms of these ideas, and the whole world is envisioned by us in terms of these noble ideas only. Nididhyasana is this condition where knowledge acquired through study and hearing, and made one-pointed by reflection and investigation, becomes part of one's nature by delving into one's own heart and making the knowledge a part of one's being. This leads to deep meditation.(translation by Swami krishnananda)
vivekachudamani verse 364(Praakarana grantha/ Shankaracharya ) śruteḥ śataguṇaṃ vidyānmananaṃ mananādapi | nidiṃdhyāsaṃ lakṣaguṇamanantaṃ nirvikalpakam || 364 || Reflection should be considered a hundred times superior to hearing, and meditation a hundred thousand times superior even to reflection, but the Nirvikalpa Samadhi is infinite in its results.
Ramana Maharshi is very recent. So of course Adi Shankaracharya used it much before. But, noone coined the term. The term has scriptural basis.
In the Brihadaranyaka Upanishad (2.4.5)
आत्मा वा अरे द्रष्टव्यः श्रोतव्यो मन्तव्यो निदिध्यासितव्यो मैत्रेयि,
आत्मनो वा अरे दर्शनेन श्रवणेन मत्या विज्ञानेनेदं सर्वं विदितम् ॥ २.४.५ ॥The Self, my dear Maitreyī, should be realised—should be heard of, reflected on and meditated upon. By the realisation of the Self, my dear, through hearing, reflection and meditation, all this is known.
Adi Sankara's commentary-
Therefore ‘the Self, my dear Maitreyī, should he realised, is worthy of realisation, or should be made the object of realisation. It should first be heard of from a teacher and from the scriptures, then reflected on through reasoning, and then steadfastly meditated upon.’ Thus only is It realised—when these means, viz. hearing, reflection and meditation, have been gone through. When these three are combined, then only true realisation of the unity of Brahman is accomplished, not otherwise—by hearing alone.
Quoting from this book - The Method Of The Vedanta A Critical Account Of The Advaita Tradition by Swami Satchidanandendra (Translated by A.J. Alston)
Chapter 3.
56. THE DIFFERENCE BETWEEN PRESCRIBED SYMBOLIC MEDITATIONS (UPASANA) AND SUSTAINED MEDITATION ON THE ABSOLUTE (NIDIDHYASANA)
It has been explained how the monk who has attained through dispassion to genuine adoption of the life of wandering mendicancy must necessarily carry out the discipline of hearing the texts and pondering over them regularly and continually until he gains immediate vision of the Self, He who does not attain this immediate vision merely from hearing, must carry out further regular hearing, supported by pondering over the meaning. Weak and mediocre candidates,'however, must also perform sustained meditation (nididhyasana, cp. T.N. at M.V, 53, intro.).
Sustained meditation, like the unbroken meditation implied in the prescribed symbolic meditations, is a piece of action. Hence it is sometimes called meditation (upasana). Yet such symbolic meditations as 'Woman is the sacrificial fire' (Chand.V.viii.l) are differently defined.
Upasana (as contrasted with nididhyasana) means maintaining a stream of identical images of which the form is (not dictated by one's knowledge of any reality but) prescribed in the Veda. Nididhyāsana, on the other hand, means fixing the mental gaze on the principle of reality to determine its true nature, like one examining a Jewel.
A candidate practising meditation in the form of upasana must select one of the meditations laid down for attaining to the Lord as associated with attributes, and maintain the same image in his mind, according to the dictates of the Veda, until he has obtained immediate vision of the object of his meditation. For meditation realizes its true end when it is used as a means to direct vision. But its reward is attainment of the Absolute in its lower form at a later time (i.e. after death) in the World of Brahma. Here there is enjoyment of the same experience as the Lord. And at the end of the world-period the final metaphysical knowledge will arise, and there will be deferred release in company with Brahma. Such is the teaching of the Veda.
The aim of the one practising sustained meditation (nididhyasana) is different. He tries to attain direct vision of reality (here in this very world) by turning his mind away from all else. And there is the difference — as against upasana — that after the rise of knowledge nothing further remains to be done. It is this sustained meditation that is referred to at Katha Upanishad I.ii.l2 by the name 'Adhyatma Yoga’. In the Gita it is sometimes called ’Dhyana Yoga' (e.g. XVI11.52). In the Mandukya Karikas it is called ’restraint of the mind’ (G.K.III.41, etc.). Its nature is described there in that latter work. Everywhere its result is described in the same way as right metaphysical knowledge, and from this comes immediate liberation (sadyo-mukti).
So basically, it looks like that Nididhyāsana is the precursor practise to that of the Patanjali's Samādhi.
Further,
Chapter 7.
Awakening to immediate knowledge of the supreme Self depending on no external factor is called Nididhyasana. It is mentioned after seeing and heairing to show that they culminate in that.... One's first knowledge of the Self is through hearing, and then one ponders over what one has heard. When heauring and pondering are complete, one comes to have immediate knowledge of the Self....
Because the use of the word 'Nididhyasana' (lit. 'sustained meditation') might lead the hearer to suppose that meditation was meant, the Upanishad deliberately uses the term 'immediate intuition' (vijnana) as a synonym for it at Brhadaranyaka (2.4.5) to show that meditation is not here meant. I already mentioned earlier how meditation amd other practices are a means to immediate experience. But immediate exprience does not exist for the sake of anything else. It is taught to be just liberation attainment of the final goal of all. (B.B.V. II.iv.217 9 220, 233-U).
Chapter 8
Sustained meditation (nididhyasana) means fixing the mind on the content of the metaphysical texts of the Veda as supported and mediated by pondering. Nididhyasana cannot here mean dhyana in the sense of upasana, for the practice of enjoined meditations for karmic merit would be useless in the present context (cp. B.Sid. p.l5^j M.V,'98,1,; ad fin,). In the text 'The Self should be seen* (B^‘had.II.iv.5)» the 'seeing of the Self refers (not to an act performed in response to a command but) to immediate awareness of the unity and sole reality of massed Consciousness, bereft of all manifestations of plurality, arising as a result of having fixed the attention on the content of the metaphysical texts.
Chapter 12
In Sri Sankara's Commentary on Gaudapada's Karikas the term 'nididhyasana' (sustained meditation) is interpreted as a synonym for restraint of the mind, practised by the middling class of students to achieve the dissolution of the mind into the Self.
Thus, the Shankaracharya's definition of Nididhyāsana is implied for the weak-minded practitioner, as an intermeditate to the Nirvikalpa-Samādhi.
As regards -
"If its contemplation, then how does constant deep thinking gives a person moksha from cycle of rebirth?"
The answer is in the Brihadaranyaka Upanishad, quoted in the begining -
To paraphrase -
The Self comes to be seen through the disciplines of hearing, pon¬ dering and sustained meditation resolutely pursued. Right knowledge of the Absolute as the sole reality only dawns when these three disciplines of hearing, pondering and sustained meditation are fused into one, and not otherwise, for example through hearing alone' (Brhad Up 2.4.5).
So, it's a step by step ladder, and doesn't happen suddenly, by just following one of step.
P.S. Your last part of the question, should be a standalone question in itself.
