Understanding the Human Mind through the Manas,Buddhi, Ahankara and Chitta as defined by the Yoga Sutras
The English  word Mind is very gross. The entire complex human mind is simplified to one  unit. That is because the western understanding of the human mind is yet very fundamental and therefore the limitations of understanding the mind using a western language. The human mind has much more  complex mechanisms and in eastern scriptures the understanding of the levels of  human thought is far more complex and extremely well understood. The fundamental  units that need to be understood and balanced in eastern philosophy are........
Manas 
It is the  lowest form of mind. Manas is thoughtless and has zero ability to “think” or  process cognitive information. The manas controls the five human senses and  functions like a binary code. It can only understand one thing from the five senses.  It understands Pain and/or Pleasure if any of the five senses feeds it pain or  displeasure. It avoids the source of the displeasure, and if any of the five  senses feeds it pleasure, it seeks to do more of it. 
It cannot  discern if something is right or  wrong, or over time  harmful to existence or beneficial to the human.
Its limitation is a simple ‘yes I want more of this’ or ‘no, I dont like this”
If you look  at most human behavior, mankind lives 80% (roughly) of his life on this level on  an average, and, therein lies all suffering of mankind.   95% of all mankind spend 80%  of their life doing things they like and avoiding things they don't like, it’s  that simple. In this material world, we spend most of our time at the level of  manas. Or spend our life in the unending pure pursuit of gratifying our senses.
Be it, the big House, big bank balance, big car or  more sophisticated forms of ego massage; I need the big job with the big title  to flash around, power to show off over other humans, to show how successful, superior and  accomplished you are. Even if this involves life long suffering, its worth it  if it brings temporary financial, power or ego benefits over other humans  around you.
Buddhi 
Now things  start to become complicated. Buddhi theoretically speaking has cognitive discriminative thought and the ability to ‘reflect’ on what manas is telling it. It is the seat  where acquired knowledge is collected and using this knowledge is able to process  information to tell you what is right or is wrong. Therefore in theory it  should have the ability to govern and override manas, by telling it, .......ok  you enjoy this, but it’s not good for you. Or say, ok you don't enjoy this but it’s  the right thing to do and it has to be done for the greater good, even if it means you have to suffer in the process.
In most humans,  there is this eternal conflict between Buddhi and Manas.  And, for most people usually manas win over buddhi. In this  eternal conflict when in most cases manas wins over buddhi, the person over  time becomes a slave to pleasures and loses his ability to think and have  governing discriminative thought. Don’t you see this all around you all  the time? In fact isn’t this how we live our lives most of the time?. Interestingly Hindu yogis  interpret the adam and eve story to be the fight between Buddhi (logic/adam)  and manas (emotion/eve) the tree being a representation of the nervous system since there was no  real garden somewhere in Israel. This is a fable to illustrate the daily tussel  in our mind between logic and emotion, and how succumbing to manas (emotion)  brings us into suffering daily. 
So now you  would say...................hey, if I keep listening to my buddhi, I will  always do the right thing, and everything will be fine. 
This is  where it becomes even more complicated, Yes the complications of the mind  are never ending, The mind is the most complicated instrument in an otherwise  simple universe, and that is why, entire humanity suffers despite nature and  the universe making things abundant for us to live a good life.
You are  aware of the stereotype of the typical ‘learned pundit’, who is hated by all, even his own  family, as he believes so strongly in his principles which are so lofty and  perfect. ......And, he lives hard by them even at severe personal discomfort  and sacrifice, and then manages to piss everyone off including his own family?
What went  wrong? Why was he so disliked for living with lofty ideals?
The  knowledge that buddhi acquires over a life time is YOUR personal data  base. This personal database is what, your individual buddhi uses to process information  fed by your individual manas. This  database is built using, information gathered by YOU, over YOUR lifetime of personal experiences,  books YOU read, experiences  YOU see others  going through in YOUR culture, YOUR society,  what was fed to YOU by YOUR parents,  and past life memories buried deeply within YOUR sub consciousness. 
In short YOUR   buddhi uses YOUR personal data base to evaluate the world from YOUR  perspective.
If you  really understand the nature of this definition..............your buddhi becomes  limited in nature.....as it is biased by the nature of your limited personal exposure,  your limited physical brain, and the limited abilities of the five senses that feel the  environment around you. There is only that much information that our brain can store for future  processing. This limitation of the input we have is what, governs and limits  the ability of the brain to do its “discriminatory” thinking. By  definition, buddhi is limiting, therefore limited, in its ability to always  take the right decision. If you pull this person out of his environment and put  him in a new one and he seems out of depth to deal with things in a new environment, or a new  situation.
Therefore the Buddha of a man is limited, and his decisions are colored by  his experiences and exposure, his society and his culture. It’s like the eye  patches over a horses eyes. Granted, by acquiring more knowledge, this field of  vision can be opened by a few degrees, but as just defined it’s still limited. It boils down  to degrees of freedom of vision.
We frequently hear, the ability of all humans over animals is the  ability to govern life through discriminative thinking. Unfortunately, most humans,  aren’t able to live like humans to be governed by buddhi all the time, talk  about evolution? The vast majority of human beings don’t live life as complete humans;  forget higher states of evolutionary thinking.
Now unfortunately this becomes even more  complex.  Preventing the Buddhi from seeing things properly and taking the  right decision is Ahankara. Or our  human ego.
AHAKANKARA 
Right from  birth, we slowly build this concept called “I” which is nothing but ahankara. The I  ‘says................I am this, and I am that.........I like this and I don't  like that..........I want others to listen to me because what my buddhi says is  right and what others buddhi says is wrong, my way is the right way, others are  wrong.................Even if the ‘I’ recognizes its limitations to take the  right decisions, it makes complex excuses to justify its shortcomings, and  invents complex excuses to say its right..........this is ego. 
The most  dangerous beast of all is the human mind. Its the most dangerous, as the  Buddhi still has the ability to correct itself with the right information. It is the ahankara  that prevents the buddhi from growing. It is the one that frequently tells  the buddhi, I am so great/wise/important/well read, I don’t need to learn  more.
It will  accept information that reinforces its definition of ‘self’ and reject all  information that weakens its self perception.................irrespective of  whether this information is right or wrong. Just or unjust.
The ahankara,  strides on the buddhi, much like a rider on a bull. This beast continuously stifles  the buddhi, and makes it operate in a way satisfying to the ego.  It will  bribe the buddhi to make the wrong decisions. It colors the lenses of the buddhi  and distorts the buddhi. The buddhi which by itself is limited by its limited  field of experience is now further distorted by ego, reducing its limited  effectiveness.
This beast   called the ‘I’ or the ego, is hard to kill, even when you try to suppress  it, by building humility, the humility by itself rears a new head by ego saying  things like, ‘look how great I am, yet how humble. Wow what an  amazing man I am! ’
It will put  up the greatest fights.............to prevent you from destroying that concept  and definition of yourself, that you call “I”.
The learned man was hated  even though he did all things right because of his ahankara.
Chitta  (consciousness) 
It has  different definitions in different contexts in the Hindu scriptures. But in the  context of what is explained above, it means your pure  untainted consciousness,  It is the divine silent observer in you. Its your divine self that is  untainted and untaintable. Its eternal. It is the real imortal you. The real  you. Realized masters identify with this imortal consciousness not the ego  entrenched, ahankara or buddhi, which are artifical constructs that lead to all  human suffering of self, and the suffering the ego creats in society.
Chitta is the bed of all living emotions or sensations. Just  living and being aware is because of your Chitta..........It  is supported by Prana, the  subtle body life force, Prana goes  where Chitta goes,  not the other way around. Prana is the substance that anchors the Chitta to the  physical body, by bringing life to inanimate matter. Citta then sits there and  brings consciousness to a human body. When someone dies, Prana goes first, then Chitta or awareness shuts down in the physical body only. But continues to  live in the universe to take rebirth .
Where does evolution and self relization come in? 
So what is  evolution of the mind? And how is it possible when so much is against you doing  the right thing in life, and everything you do getting handicapped by your  manas buddhi and ahamkara.
The first  thing you do is silence your mind.............silence the  monkey brain that can’t sit still...................the ego can’t operate, when the mind is  silent. The ego  starts to die when the mind is silent.In that silence, the Buddhi also dies. Don't think, don't judge, don't  evaluate, don't dwell on the past, don't ponder about the future, Let go of all  past impressions, opinions, worries, stresses, emotions...........just let go  of all thought..........
When you do that the  activity of the mind and its limitations die.
In this new  silence and emptiness comes in PURUSHA, or simply put cosmic awareness, with it comes the pure knowledge of the universe that is  unbounded..........limitless.......... and complete. This deep wisdom and  knowledge over-rides the limitations of time and space. It’s also called the deep meditative  state, where the mind starts to clear its debris of contaminated junk emotions,  false knowledge and false notions. The purification of the mind and its garbage  starts in that silence. 
In a sense  the more you kill the “I”  and the more the brain acquires the deeper purer knowledge that the  universe shares. The more you empty the garbage in your mind the more the place for pure divine  knowledge to exist.
This is the only way to conqueror your petty Manas, your  limited Buddhi and  your huge Ego.
That is also  why they say..............rational thinking and books don't get you to god, it  never can!
You just  have reduce your ego centered brain brain for  the greater knowledge to flood  you.
The author is Sanjay Rao. In  search of the ultimate truth beyond concepts and notions, in that silence,  after 20 years in soulless corporate board rooms. 
  https://twitter.com/#!/sanjayrao1010