The Gay Science
Nietzsche's many works spoke of a Master-Slave Morality, The Will to Power, or something stronger that overcomes the weaker and Darwinistic adaptation and will to live. Nietzsche expressed his moral philosophy throughout his collection of works; the most important of these to secular ethics being "The Gay Science" (in which the famous God is dead phrase was first used), "Thus Spoke Zarathustra", "Beyond Good and Evil" and "On The Genealogy of Morals".