Jacob + MIB = ?????
Yin and Yang is used to show how opposites in the world are dependent on one another to exist. Apparently it is not so much about good and evil, but about the balance between those 2 opposing things. . Dogen said that Locke/MIB is evil incarnate meaning that he is pure evil and since he is Jacob’s rival we can probably say that Jacob is all good. What if Jacob and MIB are the good and evil inside of one person, but have become physical entities on the island .
When they are on the beach MIB says to Jacob “Do you know how much I want to kill you?” . But Jacob knows he can’t because they need each other, because they are apart of each other, it would create an in balance within whoever they came from. Maybe that’s why MIB doesn’t have a name yet.Â It makes sense that they both are aware of where they came from and Jacob is more accepting and the MIB wants a way out to be free and do whatever he wants. MIB’s loophole was to find someone whose body he could fill with pure evil and that happened to be Locke, why Locke is so special I don’t know .
I think the little boy that MIB and Sawyer saw is Aaron and that MIB and Jacob are embodiments of two opposing forces inside him (at the risk of misinterpreting Yin and Yang we will say Good and Evil). MIB and Jacob are like the angel and devil sitting on Aaron’s shoulders . This is why the little boy told MIB that “you can’t kill him”  Since they are one in the same they can’t kill each other, because they would end up killing themselves. He will never be able to get rid of all the good that was in Jacob or even in the world for that matter, because no matter how much bad things happen there is always hope that some good will come. 
 Brother, My. “Conversation I Had With Him, Probably After He Read Doc Jensen”. March 3, 2010.
 Faraday, Daniel. Faraday’s Journal. Widmore Industries, ????, 1954, 1974-77, 1996-2004.
 Fromtheblackrock, Firstmate. Dairy from the Black Rock. Hanso Foundation, B4TSR
 Radzinsky, Stuart. Swan Station For Dummies, The Island : Dharma Initiative, 1980
 Troup, Gary. The Bad Seed. Unpublished, 2004.
 Wantstomakechanges, Whoever. “Yin and Yang”. [Online] www.wikipedia.com, March 3, 2010.