When prior knowledge is given in the form of a prior, Bayesian method is the rational way of making decisions, based on Cox' arguments. However, prior knowledge doesn't usually come in a form of a prior. For instance an expert may say that X and Y are independent, or that increasing value of X will influence Y to increase. We need to figure out how to use those kinds of knowledge to bias our learners, and this is where Knowledge Intensive Learning comes in. Eric Altendorf does research in the area and is doing a series of posts on it in his new blog.