Do we know anything?

Every once in a while, I have an existential crisis about whether or not we can ever know anything (in the social sciences, that is). The genesis is almost always reading an article (e.g., Why most published research findings are false) or blog post (like the timeline at the bottom of this post by Andrew Gelman) about the lack of empirical evidence for even popular theories once statistical issues in the original papers have been corrected (compounded, of course, by the publication bias, researcher degrees of freedom, etc.). 

There is a wonderful clip of the great physicist Richard Feynman talking about "pseudoscience" (which seems to include the social sciences in his view). I think that this was originally aired as part of a BBC or PBS special. In it, he says the following:

Now, I might be quite wrong. Maybe they [so-called "experts" in social science] do know all those things. But I don't think I'm wrong. You see, I have the advantage of having found out how hard it is to get to really know something, how careful you have to be about checking your experiments, how easy it is to make mistakes and fool yourself. I know what it means to know something. And, therefore, I can't...I see how they [social scientists] get their information, and I can't believe that they know it. They haven't done the work necessary, they haven't done the checks necessary, they haven't done the care necessary. I have a great suspicion that they don't know [what they think they know] and they're intimidating people by it. I think so. I don't know the world very well, but that's what I think. 

Although Feynman is quite harsh in his criticism and one could easily throw up one's hands in defeat after reading this, I always find this quote comforting. Even if we don't really know what we think we know, things are not, in principle, unknowable. In other words, there's always hope.