Full Idea
Since awareness of defeasibility issues is an essential prerequisite for any genuine perceptual knowledge of even straightforward physical objects, any realist theory of perception must be indirect or representative, rather than direct.
Gist of Idea
Direct realism is false, because defeasibility questions are essential to perceptual knowledge
Source
David Galloway (lectures [2007]), quoted by PG - lecture notes
A Reaction
[a very compressed summary] A very interesting claim. The issue might be over what direct realism is actually claiming. If it claims full-blown knowledge, then the criticism seems good. But it might survive if it claimed rather less.