In 1875-79, Nietzsche turns to the philosophy of the 'free spirit', elaborating thus an original ethic. Our aim here is both to analyse the formation of this new ethic and to show that this ethic can be defined as an ethic of self assertion and alleviation of life - an alleviation which doesn't consist in breaking with weightiness, but in controlling it and playing with it. The emergence of this philosophy of alleviation goes with a deep transformation of Nietzsche's ideas of religion, art and knowledge, as well as a transformation of his interpretation of Schopenhauer and Greek pessimism.