Namaste Anirudh

Originally Posted by
Anirudh
Can you define the two terms a) Self Realization b) Moksha in simple terms.
It seems to me that you ask questions even though you already know the answer to them. 
Here are a few verses from the scriptures that illustrate these questions and provide an answer to them:
"That God, the maker of all things, the great Self, always dwelling in the heart of man, is perceived by the heart, the soul, the mind; -- they who know it become immortal." (Svetasvatara Upanishad 4.17)
"The wise who perceive Him (the one God, the one ruler of many) within their self, to them belongs eternal happiness, not to others." (Svetasvatara Upanishad 6.12)
"This (God), which rests eternally within the self, should be known; and beyond this (God) not anything has to be known."
(Svetasvatara Upanishad 1.12)
Self Realization per vaishnava understanding means two things:
1) to know ourselves as an individual soul who has an eternal relationship with the Supreme Lord
and
2) to know the Supreme Lord (God).
In every person there are two souls (two selves): we individual soul (individual self called jiva or jiva-atma), and the Supreme Lord (God) who is Supreme soul or Supreme Self (the Self) called paramatma.
In the above verses Supreme Lord (God) is denoted as "Him", "God", or "Self", and sometimes in some translations as "Supersoul", whereas the individual soul is denoted as "self".
So, this Self Realization denotes both of those two things: to know ourselves (the self, jiva) as a being in relation to the Lord, and to know Him -- the Lord (the Self, paramatma).
In the above verses this Self Realization is denoted as knowledge of, or realization of the Lord: "who know it ", "who perceive Him", "should be known, ... has to be known".
Moksha (also called mukti) is liberation from repeated births and deaths. This moksha (mukti) is permanent and eternal state of liberation which the jiva soul attains because it is said to be the state where one "become immortal", and attains "eternal happiness", and "one never returns" (one never returns from this liberated state back to this repeated births and deaths of this material world).
This is seen in the above verses where this moksha is denoted as "become immortal", "eternal happiness", and sometimes in some verses as "he is not born again", and "place from which, having attained it, one never returns" (see below examples of verses from the Bhagavad gita and Katha Upanishad).
The state of moksha follows as the result of Self Realization.
See above verses:
"That God, ... the great Self, ... -- they who know it become immortal."
"The wise who perceive Him ... within their self, to them belongs eternal happiness, not to others."
The state of moksha (mukti) is experienced in the world that is called Vaikuntha, which is a personal residence of Lord Vishnu, sometimes called the Highest abode of Vishnu (viṣṇoḥ paramaḿ padam) mentioned in the Katha Upanishad 1.3.9 and Rig Veda 1.22.20.
One of the features of the state of mukti in addition to the immortality is the experience of (feeling of) eternal happiness (unending happiness) which is experienced by the mukta (liberated soul). This is stated in the Svetasvatara Upanishad 6.12 (I mentioned above):
"The wise who perceive Him (the one God, the one ruler of many) within their self, to them belongs eternal happiness, not to others."

Originally Posted by
Anirudh
I think self realization precedes moksha, if so is it possible for a self realized soul to fall back into the darkness of ignorance again?
Yes it is possible, but one who is a self-realized soul who has completely took a refuge in the Lord, to him the Lord gives a promise that he will reach the realm of Vaikuntha, and not to return to this mortal world again:
Bhagavad gita 8.15:
"After attaining Me, the great souls, who are yogīs in devotion, never return to this temporary world, which is full of miseries, because they have attained the highest perfection."
Bhagavad gita 8.21:
"That which the Vedāntists describe as unmanifest and infallible, that which is known as the supreme destination, that place from which, having attained it, one never returns -- that is My supreme abode."
Here the Lord's abode is described as "the supreme destination" and "place from which, having attained it, one never returns" which tells us that this is a place of liberation (or mukti because it says "one never returns"), which is the ultimate goal for every yogi (because it says "the supreme destination"), and also it is (see above verse 8.15) "the highest perfection" to achieve Him -- Lord Krishna there in his abode.
After death everyone achieves some destination, higher or lower species of life, higher or lower world, but here in these verses Lord Krishna says that his supreme abode is known as the supreme destination which means that there is nothing higher than this because it is the supreme destination for every yogi to be achieved, and also it is "the highest perfection".
What is higher than "the supreme destination" and "the highest perfection"? Apparently nothing because there is nothing which is higher than the highest.
There are several other verses in the Bhagavad gita that tells the same, that one never returns. See eg verses 8.16; 15.6; 13.24; 4.9; 15.3-4.
Vaikuntha (the Highest abode of Vishnu) is permanent and eternal state of liberation (mukti), which is the ultimate goal for every yogi who:
"reaches the end of the journey, the Highest abode of Vishnu" (Katha Upanishad 1.3.9)
and also
"he reaches indeed that place, from whence he is not born again." (Katha Upanishad 1.3.8)
Here in the Katha Upanishad "the end of the journey" and "he is not born again" tells us that this viṣṇoḥ paramaḿ padam "the Highest abode of Vishnu" (called Vaikuntha in the Puranas) is a place of liberation (or mukti because it says "he is not born again"), which is the final and ultimate goal for every yogi (because it says "the end of the journey"), and it says that it is the highest possible abode to be achieved by a yogi because it says that it is "the Highest abode of Vishnu" where "the Highest" means that there is no something higher than that.
This is also confirmed in the final verse of the Chandogya Upanishad: " ... (he) does not return, yea, he does not return".
I know that you are interested in the Ramanuja's tradition of Sri vaishnavas. So I can tell you that in the commentary on the Bhagavad gita 18.62 (tam eva śaraṇaṁ gaccha ... ) Ramanuja explained words "eternal abode" (sthānam śāśvatam)
mentioned in the verse 18.62 to refer to the Lord Vishnu's abode by quoting several Shruti texts including those two that I mentioned above, Katha Upanishad 1.3.9 and Rig Veda 1.22.20, thus giving a proof from the Shruti that this is the final destination that a yogi has to reach and the place of eternal liberation from which there is no return to this mortal world again.
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Svetasvatara Upanishad and Katha Upanishad quotes see at http://www.sacred-texts.com/hin/sbe15/index.htm
Bhagavad gita quotes see at BBT, vedabase
regards
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