UC Berkeley

The law of equal innervation of the two eyes, positing that conjugacy of movement of our two eyes is basic and innate, was enunciated in Hering's 1868 persuasively argued monograph. It has prevailed over Helmholtz's contrary view that conjugacy is learned. Yet 100 years earlier, Thomas Reid (1710-1796), Scottish clergyman and professor of philosophy, advanced exactly the same view as Hering, using almost identical arguments. Reid also considered whether the eyes' parallelism might have its origin in "custom" or "habit" rather than "nature" and reached the now accepted conclusion that it is innate.