In the Star Wars series, this concept finds mention multiple times. Jedii warriors are people with special powers, and they defend the good people. Siths on the other hand are equally powerful people, but are dark and bad.
Darth Vader, the most powerful Jedi, turns into a sith in 'The Revenge of The Sith.' Before his becoming a sith, he used be a Jedi named Anakin Skywalker. He remains equally powerful -- infact grows in his power. But he no more remains a Jedi.
What differentiates a Jedi and a Sith? It's the concept of dark forces. Sith's give themselves up to the dark forces. Jedis don't. That's the difference.
On the face, the concept looks absolutely simple. Quite on the contrary, it most probably is based upon a very profound philosophical thought. I also sense that it's been deeply inspired by Hindu philosophical concepts.
When Anakin is introduced to the Jedi council as a prospective Jedi, Jedi Master Yoda has something quite insightful to say. Although Anakin is full of the powers needed to be a good Jedi, Yoda senses a deep sense of fear in him. 'Fear leads to anger; anger leads to hatred; and hatred leads to war.' He says, and reconsiders inclusion of Anakin as an apprentice inspite of his being a prodigy. Anakin is, however, eventually accepted into the Jedi council. He proceeds to become the most powerful Jedi that had ever been. But his fear, one of the dark forces, is constantly at work within him. And finally, in the moment of test, he loses his integrity and passes into the dark side. The Sith Lord rechristens him as the 'Darth Vader.' And while he's luring Anakin to turn into a sith, he says: 'Learn to use the dark side of The Force.'
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There is a mention of 'The Force.' And the dark forces are as much a part of this Force as bright forces are. Dark side of the Force are fear, anger, hatred, jealousy, pride, greed. Bright side of the forces are love, serenity, self-control. Both are sources of enormous powers. In a beautiful shot scene, the Darth Sidious is trapped by Jedi Master Mace Windu, and a severe fight ensues. The sith powers, arising from the dark side of the Force, are a good match for the Jedi Master's powers. But there is one difference. While the good and evil forces meet with each other, moment by moment, the Sith Lord suffers a severe decay. Within seconds of combat, Darth Sidious turns from a powerful figure into a crumpled, wrinkled invalid. Master Windu, however, remains unscathed. I could sense a very clear indication of the fact that dark forces are powerful, but they cause a decay from the inside. While dark forces might add to the immediate power and results, they invariably eat away the inner health.
This is the point where the discussion could be seamlessly transformed into Hindu philosophy.
(Much of the material below are more my interpretation; not verbatim translation of the scriptures. So, it would be a good idea to take things with a pince of salt. But the better thing about the following matter is that I am ready to be believed or disbelieved; to defend refutation modestly on an intellectual level)
In that, it's said that three kinds of forces reside in us: Saatwik, Raajsik and Taamsik. Instances of Saatwik forces are love, intelligence, alertness, love, peace, etc. Instances of Raajsik forces are aggression, determination, courage, eroticism etc. Instance of Taamsik forces are fear, hatred, jealousy, laziness, selfishness, greed etc.
Saatwik forces are outright good; Raajsik ones are neutral; and Taamsik ones are outright bad. The ancient caste system of India was partly based on this. Brahmins (researchers, doctors, priests) were supposed to be pure saatwik characters. They would pursue knowledge and spread it among able disciples, would lead a simple and ascetic life, would never accumulate wealth, and would generally be agents of connecting the rest of the humanity with the higher world. Khrathriyas (rulers, judiciaries, warriors) came next. They are mostly saatwik, but would have raajsik elements in them. Their saatvik character would give them the ability to think and the love for their people. Their raajsik character would give them the power to defend their state if need arose. Vaishyas (traders) came next. They had an equal mix of all forces. They would handle their business with intelligence and energy, which are saatvik forces. The aggressiveness required to defend their wealth emenated from raajsik sources. The greed, which is inherent in all trade adds that dash of taamsik force into the vaishya. Shudras(slaves, labourers, butchers, janitors,...) are predominantly taamsik. They aren't intelligent. They are not courageous. They don't feel for others. They don't have the self-respect to stand up against oppressive forces. They are lazy, unalert and uninnovative. Their only motivation towards working is greed, fear (of punishment and starvation).
The caste system was abused for centuries. Caste was never an inherited wealth in its original form. It had to be earned through conduct and good living. Its running in the lineage might have been authentic many centuries back. But, bloods mixed and matched beyond all account. There's no more any purely Brahmin blood, Kshatriya blood, Vaishya or Shudra blood. We are all born to an unknown lineage of virtues and vices. Today, each man has to prove for himself what he is. We can't borrow any discount from our lineage, since it doesn't exist. Moreover, considering the economic system of today, we all are part Brahmin, part Kshatriya, part Vaishya, and part Shudras.
These forces have also been said to have connection with our lifestyle. For instance, vegetarianism is said to enhance saatvik elements in our being, while non-veg, alcohol and other addictions are supposed to enhance raajsik and taamsik elements. One of the reasons why brahmins have mostly been forbidden from eating non-vegetarian food. The varying levels of ascetism they are supposed to observe also has a similar reason : simplicity enhances satwa; materialism subdues it giving place to tamas.
In parting, the beauty of the idea must be noticed and appreciated. Could it be an experiment worth carrying to keep a probe as to which tendencies are at work at various points of our day-to-day life when we are working, sleeping, talking, eating etc.? Are there such supermen present who lead an active and productive life without ever borrowing energy from the taamsic elements (the dark side of the force). Are there people who can be active, courageous, productive, creative just because they have discovered and opened up the vast reserves of saatwik forces (Bright side of the Force) inside them? Are there true Jedi warriors found these days?
And more interestingly, whether they exist or not, the question is: Can we live a life driven completely by saatwik elements? Can we purify ourselves to become true Brahmins?
I think, it's worth giving a shot!