Horseshoe theory

The horseshoe theory asserts that the far-left and the far-right on the left-right political spectrum are not on the opposite and opposing ends of a linear political continuum. Rather, they closely resemble one another, analogous to the way that the opposite ends of a horseshoe are close together. The theory is attributed to French philosopher and writer Jean-Pierre Faye. Proponents of the theory point to a number of similarities between the far-left and the far-right, including their supposed propensity to gravitate to authoritarianism or totalitarianism. However, the horseshoe theory has also received criticism. The criticism is described on the English WIkipedia page: Horseshoe theory#Criticism.

Relation to the Eysenck model
The 20th-century psychologist Hans Eysenck described something similar, with radical-conservative and authoritarian-democratic axes, in an effort to illustrate perceived similarities between Nazis and Soviets located at opposite reaches of the classical spectrum. The U-shaped plot of Eysenck’s diagram is congruent with the “Horseshoe Theory,” in which the traditional spectrum bends so that the left and right wings approach each other, two opposites attracted by their mutual distance from the political center.