Another skeptical argument begins from the undeniable fact that things sometimes look other than they are. If my friend’s red shirt looks grey in the dim light, the shirt itself isn’t grey, but surely something is, surely my experience is of grey. And if what I’m seeing in the dim light is that grey thing, a visual impression, and this act of seeing doesn’t feel any different from my usual acts of seeing in ordinary light, then maybe all I ever see are these impressions. But if I only see impressions, if I never actually see the world itself, how can I know that it’s out there? The second lecture will examine the allure of this style of argument.