Question

When an economist attempts to apply conclusions from a two good model to the real world, they break the chain of _____________ logic?

Answer 1

To break the chain of circular reasoning, the economist gives two models with different premises and leads to one conclusion. Providing different premises that lead to one conclusion can strengthen an argument. 
Circular reasoning is a chain, a logical fallacy of the argument that has the same premises which are also the conclusion of the person. Sometimes, the words are just written or said differently but still has the same point.