No one can once doubt but existence and non-existence destroy each other, and are perfectly incompatible and contrary.
 David Hume, A Treatise of Human Nature (1738). copy citation

add
Author David Hume
Source A Treatise of Human Nature
Topic existence doubt
Date 1738
Language English
Reference
Note
Weblink http://www.gutenberg.org/files/4705/4705-h/4705-h.htm

Context

“When any objects resemble each other, the resemblance will at first strike the eye, or rather the mind; and seldom requires a second examination. The case is the same with contrariety, and with the degrees of any quality. No one can once doubt but existence and non-existence destroy each other, and are perfectly incompatible and contrary. And though it be impossible to judge exactly of the degrees of any quality, such as colour, taste, heat, cold, when the difference betwixt them is very small: yet it is easy to decide, that any of them is superior or inferior to another, when their difference is considerable.” source