Trigger Happy

Shoot first, ask questions later

- STEVEN POOLE

The extramission theory of vision was once all the rage. Plato argued that we are able to see the world around us because beams shoot out of our eyes. The gods, he has Socrates explain in the Timaeus, caused “the pure fire within us, which is akin to that of day, to flow through the eyes in a smooth and dense stream”; when this eye-fire meets daylight it coalesces into a visible substance along the beam-path. We can’t see at night, obviously, because our eye-beams do not meet a similar phenomenon (sunlight) with which they can combine.

Unfortunately, advances in anatomy and optics by Isaac Newton et al eventually proved this poetic idea wrong in its particulars. But a more abstract version of it lived on in philosophical idealism, according to which the real world we suppose we see around us is actually a creation of our minds. The 18th-century Irish bishop George Berkeley coined for this idea the snappy slogan “esse est percipi”, or “to be is to be perceived”: as long as a thing is not seen by humans (or at least God), it simply doesn’t exist at all.