How did Vito know?

A very basic, fundamental question that surely must have been raised on this forum more than once before, though I can find no evidence of it: During the latter part of GF1, after Michael had assumed full control of the Corleone family and begun the family's transition to Nevada, Vito warns Michael of an impending assassination attempt against him. Not only can Vito foresee that the attempt is coming, he is also able to furnish Michael with important details, i.e. that the attempt will be initiated by Barzini, that it will occur at a meeting, set up by someone close to the family, whom Michael absolutely trusts, thereby guaranteeing his safety.

Simply, how did Vito know all this? That Barzini would be the culprit is somewhat logical, but for the fact that the Corleones would soon be leaving New York anyway - which Barzini would already know about from Moe Greene, who "talks to Barzini" - thereby no longer presenting any challenge to Barzini's interests. So why murder Michael, when the Corleones are already "getting chased out of New York"?

Even more to the point, how could Vito have known the manner in which the assassination attempt would be carried out, with such specificity? I can't even speculate about the answer(s) to that, other than to guess that it's rooted in some kind of Mafia custom or "standard operating procedure" that goes back to the Mustache Pete era.

Thoughts? Ideas?

Very simple. It's what Vito would have done had he been in Barzini's situation. (In the book it's explained that Vito did this to the Maranzano character years ago).

Vito wouldn't have been able to predict all the details but with 30 yrs + experience he would have known that like most such attempts, the murder of Michael could not have been easily accomplished without betrayal. It was just a question of who.

Also remember that although it was unspoken, everyone in the family blamed Carlo for Sonny's death though they pretended not to do so. In that instance they had been fooled once. They weren't going to be fooled again by Barzini.

I don't know if it's a Mafia custom other than pure pragmatism. Your "friends" are the ones who set you up/kill you because they are the one who can most easily get you relaxed, alone and unguarded. As Vito said, it's an old trick.

An even simpler answer: directoral license. It was convenient for Puzo and FFC to have Vito make those predictions in order to set us up for the denouement--especially that nice scene where Tessio lights Barzini's cigarette and makes his pitch to Michael.

Closer to logic: Barzini had been signaling bad intentions by crowding the Corleones (as in Tessio's beef in the fishtank scene). And, Barzini knew that the Corleones' move to Nevada would still leave a Corleone family, allied with Michael, in NY, and still rivaling Barzini's family. So, I don't think Vito was being overly prescient in his predictions. And, as Lilo said, in the Mob, it's always your friends who do you dirty.

What really puzzles me is why Vito didn't know, until after the Commission meeting, that it was Barzini all along. "Tattaglia is a pimp - alone he could never have outfought Santino." Sure, Vito - and that was true before the Commission meeting.

Even Moe Green thought the Corleones were being run out of New York by the other families, and that Barzini was now the Don with whom he needed to deal. Vito knew that the Corleones were (wrongly) perceived as weak, and he also knew that someone within the family would betray Michael to Barzini. It was not a stretch for Vito to understand that once he died and Michael was officially head of the family, Barzini would rub him out and take over. Given that there would be a traitor, it makes sense that the traitor would not let on to what he was doing until Michael was out of the way. It came as no surprise to Michael when Tessio approached him about how the meeting could be held on his territory where Michael would be "safe." Vito, with his Sicilian cunning could have easily figured this out. If there is directorial license in this I think it is to tell the viewing audience of what was coming. My guess is Michael had already figured all this out on his own, and was humoring Vito by allowing him to give him this warning.

I don't think it's all that complex. As intended, the NY families perceived the Corleones as weak and vulnerable. As a hugely experienced Don, Vito could figure on a probable scenario. I don't think Vito was particularly prescient about it. If at the height of Corleone power, Sollozzo felt comfortable making a move against the Corleones, why not make a move now that the Corleones were at the perceived nadir of power.