Full Idea
The space of science is neutral as between touch and sight; thus it cannot be either the space of touch or the space of sight.
Gist of Idea
Space is neutral between touch and sight, so it cannot really be either of them
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 3)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.14
A Reaction
I find this persuasive, although it is hardly a knock-down argument. It is a very simple problem for anti-realists, that if you say reality IS sensations (à la Berkeley), then you have conflicting sensations of what seems to be one reality.