The Data of Ethics is a fascinating exploration of the concepts of good and bad conduct, that looks at the problem from sociological, psychological, and biological viewpoints.
Boethius, William James, Thomas Paine, Paul Henri Thiery Holbach, Austin Holyoak, Baruch Spinoza, Hastings Rashdall, Edward Caldwell Moore, Frances Power Cobbe, Herbert Spencer, H.R. James, M. De Mirabaud & R.H.M. Elwes