First a definition

The foil in literature is the character that offsets the main character to help emphasize the main character while detracting the main character's faults with their own. It's most commonly recognized though in comedic duos like Laurel and Hard, Abbot and Costello, Amos and Andy, Fred and Barney, etc. One character is the leading man who is supposed to be the smart lead that does everything right while their partner is the bumbling fool. In comics it's the sidekick to the hero. It's also the straight man. You get the picture.

So the MC foil is the one in the group that's of lesser skill or presence who holds it down, but isn't supposed to be as good as the lead MC. It works well for a number of reasons. Multiple voices help in hip-hop because it helps draw attention to the spit as the voices change rather than seeming like a run on sentence. Only MC's of certain caliber can really hold that lane down. And not all of them want to.

Let's be real. It's impossible to spit 100% 100% of the time. Over the course of an album by example... really hard to do. But if you're only responsible for 50% of the spit on the album, well that makes it a lot easier to appear to come of 100% 100% of the time. This is the technical reason a solo artist with solo albums they hold down under their belt is more impressive than an artist in a group with the same number of albums. But that was a tangent.

The foil is the person dropping that other 50% and they have to be able to hold their own too. But it's a contrast to the lead MC. How about some examples:

Public Enemy - perhaps the most divergent pairing, but it really worked. Would Chuck D have been able to do half the stuff he was able to do if Flav wasn't offsetting him, just by being Flav. I mean do you remember Mista Chuck?

Outkast - I always say there wasn't a foil on the first album, and that the majority of folk couldn't even tell them apart. It managed to work for them because of their own uniqueness but by the second album it was becoming clear the differences between them. It's debatable who was the foil. I mean people obviously want to say Dre, but when you think about it, Boi has been the same character througout, while Dre has become a 'character' even if it is who he really is.

Organized Konfusion - Pharoah fucking Monch. Perhaps one of if not *the* greatest lead in a duo of all time. I actually think a Flav like character for him could have worked better than his solo effort. As far as Organized was concerned though Prince Po has to be the hardest working foil ever. But in the end it kind of worked against him.

The Roots - Black Thought may be second behind Monch. But on the real Malik B could have been just as good but Thoughts work ethic kept him at the top. Post Malik there was a lot done to offset Thought. Of late the whole MMJB have been integral in that, and it's good because it really does allow him to be the Alpha male.

Wu-Tang - It's up for debate, and equally up for grabs as to who is the lead. RZA is the leader, but who is the lead MC changes track to track. I think the battling for that top slot is what makes them work together well as a unit of all Foils.

Tribe - It's always been Tip despite the fact that he has more foil like characteristics. Phife was barely on the first joint. Then started coming to his own on the second. Actually I think at the heart of the beef is that Phife always wanted to be the lead. Didn't really want to accept the foil role. Part of that because of the reaction to him coming out of Low End. Everyone gassed his head to believe he could be the lead. But he never had the work ethic to do it, while Tip was steady grinding.

I'm gonna stop here. Feel free to add on.
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