 The move to what is often referred to as mid-level theorizing was (partly) a result of the challenges with high theory just discussed, and manifested most prominently by the 1979 publication of Tom Beauchamp and James Childress’ influential Principles of Biomedical Ethics (PBE). The approach set out in that book, and its revised versions appearing in the book’s subsequent editions, feature mid-level moral norms, which take the form of four moral  principles.[6]  Beauchamp and Childress’ four principles are: