Duverger's Law

i want to get really academic nurty right off the bat in this pot and have you explain a duverger's law. The standard model in our mind is two party competition, yes, no choice. But when there are actually multiple options, as some of these primaries, or sometimes in a presidential election, then the electorice can fracture across all the options. And we kind of think that the winner has a mandate by having the most votes, but not necessarily because a majority might have really wanted the plurality winner to lose.