The essence of my thesis is that a great many factors that contribute to partisan divisiveness are common to all humans regardless of ideology – things like the confirmation bias, tribalism, hypocrisy, and on and on – and that the actual number of things that separate left and right are small, but their effects are huge. Those things, I suggest, are 1) Moral Foundations, and 2) Cognitive Style.
As for cognitive style, I suggest there are two, described by Arthur Herman in his book The Cave and the Light: Plato Versus Aristotle, and the Struggle for the Soul of Western Civilization in which Plato and Aristotle serve as metaphors for them. Here’s a quote from that book:
By the time we close the last pages of the Politics, we realize we are standing on the brink of two different ways of thinking about governing human beings. Politics on Plato’s terms becomes prescriptive, a series of formulae for shaping man and society into what they should be rather than accepting things as they are. Politics on Aristotle’s terms will be largely descriptive, in which the more we discover about human nature, the more we recognize our powerlessness to effect real change.
Here are three sentences which convey a central idea of my theory of cognitive style:
1) Cognitive style is organized in advance of experience
2) it is not true that Plato and Aristotle invented contrasting epistemic systems out of thin air
3) it is true that each man merely articulated the system with which he was born.