First, and most importantly, I want you to re-watch the all important 1st scene of the Season 5 finally, "The Incident".
The producers have already said we have seen the answer, we just didn't know what we were seeing. Jacob is one being with two sides. We have the evidence, shown but basically missed when we saw it.
The Man In Black is Jacob; that is why they did not tell his name. He is one entity, one side good, one side evil (as Dogen said). Watch the scene again. We already know the MIB is the smoke monster; listen to the noise created by Jacob's spinning wheel in that first moment of the scene. It IS the sound of the Smoke Monster. Of course it is. He's Jacob AND the Man In Black...AND Smokey.
Once the scene with them talking starts, notice the BIG giveaway...they are never seen engaged face to face...when one talks, the others shadow in in the frame; white Jacob talks, his dark side lingers in frame and vice versa; they are TELLING us...it's the two sides of the one being...his two sides are debating the internal struggle. SO DELIBERATELY SHOT that way!!! Watch as Jacob says "...just progress"...the two have their heads pointed in the exact same direction out at seas...as he finishes, their heads move across each other...same position heads...same guys...internal conversation.
HUGE TIP OFF I JUST NOTICED!!!!! Jacob asks "Do you want some fish?" as he finishes his last mouth full. "I just ate" answers the MIB. Of course he did...we just watched him eat!!!! Jacob just ate his last bite!!!
100% convinced. Thoughts?