Science enjoys a lot of respect these days, if not always for the social value of its results then at least for the rigor and precision of its methods. It is an honor to say of a study or an argument that it has been done scientifically. This must be because we think that, in general, science and scientific methods are effective for getting at the truth. If pressed to articulate these feelings we might start by saying that the careful, accountable, and methodical approach of science prevents, as much as possible, the influence of personal bias, superstition, sloppiness, whimsy, sloth, and other human weaknesses that obscure the truth. Thus, when we claim to have done something scientifically, we speak with the authority of a truth-generating enterprise.

There has to be more to it than just being careful (careful to do what?) and accountable (accountable by what standards?), and we can appropriately ask why science has its special status as a supplier of knowledge about the world. Thus the unifying question in the pages that follow is, Why should we believe what science says about the world?

This is a question of justification of scientific knowledge. It asks not so much about what science claims about the world but more about how science proves what it does claim and why it gives us reason to believe that these claims are true.