You can find part 1 here, part 2 here, part 3 here, and part 4 here.
More could be said about the scientific and philosophical shortcomings of the works mentioned in the previous article (see part 4). However, my goal was merely to hold them up to the framework of Hare’s moral gap (see part 2).
Three things should be evident.
First, moral theorizing has two gaps that will at some point need to be bridged: the gap between ought and can and the gap between ought and is. That is to say, a good moral theory will need to address the disparity between moral demand and our natural capacities, what we ought to do and what we are able to do. Also, it will need to do this without attempting to derive a normative conclusion from purely descriptive premises.
Second, there is within naturalism an inherent epistemic dependence on science as the chief, if not the only, source of knowledge. This presents a looming problem for any naturalist attempting to build a moral theory grounded in purely scientific terminology and methods.
Third, scientific attempts to bridge the moral gap have taken on strategies that are ultimately flawed. While they are extremely valuable in describing moral ideas and behavior, they are ultimately unable to deliver an essentially prescriptive understanding of morality.
James Hunter and Paul Nedelisky provide us with a helpful metaphor. They compare scientific explanations of morality to a metal detector, which “cannot tell you everything about what’s buried at the beach, but it can tell you about the buried metal things.”[1] I will take the liberty of extending the analogy. A metal detector can tell you that there are coins buried, but it can not tell you how much they are worth. The trade-in value of any coins you find must be determined by someone who is an expert, someone whose expertise is based on his own collection of valuable coins that far exceeds your own, and someone who is able to pay you for the coins you have. Let the reader understand.
[1] Hunter and Nedelisky, Science and the Good, 11.