Social constructionism, constructivism, post-structuralism, standpoint epistemology, deconstructionism….ever heard of these? Chance are, if you’ve taken a look at some of the recent literature in the philosophical aspects of librarianship, you’ve come across these and/or similar theories. Variously lumped together under the aegis of postmodernism, these theories are distinct, yet they are united through a common belief that we have no epistemic access to a mind-independent reality. Some of these theories go even further and claim not only that we can’t know anything about the world outside of ourselves, but that there isn’t even an objective, mind-independent reality at all—reality is subjective. In effect, these theories advocate various forms of relativism. I’ve criticized this type of relativistic thinking in previous posts, but perhaps it’s time to clarify. Specifically, I want to explain why relativism, in all of its forms, is harmful to librarianship. This type of thinking is self-refuting, it impedes learning, it disenfranchises those who most need our help, it obstructs social progress, and it erodes the value of libraries in society.