  The main achievement of Moore's early period is his book Principia Ethica. It was published in 1903 but was the culmination of the reflections which Moore commenced in his 1897 dissertation on ‘The Metaphysical basis of Ethics’. The main impetus, however, came from a series of lectures in London on ‘The Elements of Ethics’ which Moore gave late in 1898. Moore had the text of these lectures typed up with a view to publishing them; but as his thoughts progressed he reworked his text and Principia Ethica is the result of this reworking (the lectures have recently been published as The Elements of Ethics). Most of the first three chapters come from the 1898 lectures; whereas the last three chapters are largely new material.