Unconscious inference

Unconscious inference (German: unbewusster Schluss), also referred to as unconscious conclusion, is a term of perceptual psychology coined in 1867 by the German physicist and polymath Hermann von Helmholtz to describe an involuntary, pre-rational and reflex-like mechanism which is part of the formation of visual impressions. While precursory notions have been identified in the writings of Thomas Hobbes, Robert Hooke, and Francis North (especially in connection with auditory perception) as well as in Francis Bacon's Novum Organum, Helmholtz's theory was long ignored or even dismissed by philosophy and psychology. It has since received new attention from modern research, and the work of recent scholars has approached Helmholtz's view.

In the third and final volume of his Handbuch der physiologischen Optik (1856–1867, translated as Treatise on Physiological Optics in 1920-1925, available here), Helmholtz discussed the psychological effects of visual perception. His first example is that of the illusion of the Sun rotating around the Earth:

Every evening apparently before our eyes the sun goes down behind the stationary horizon, although we are well aware that the sun is fixed and the horizon moves.