Green's contributions to philosophy were partly constructive, partly (and perhaps mainly) critical and destructive. On the critical side, his greatest effort was his attack upon the philosophy of Hume in two masterly Introductions to an edition of Hume's 'Works,' published in 1874-5. English philosophical thinking, so Green held, had stuck fast in the scepticism of Hume. Such forward movement in thought as there had been since the 18th Century, had come mainly through the writings of men like Wordsworth and Shelley--men who having seen deeply into life, had expressed themselves in imaginative, not in philosophical ways. To set the stagnant tide of speculative thinking in motion, involved a two-fold task: on one side the breaking down of the barriers erected by the sensationalist and materialist schools of the 17th and 18th centuries, and on the other side the letting in of a current of fresh ideas from some source outside of England. The first, or destructive, task Green performed with remarkable success in the two Introductions. For the new and truer ideas which were to displace the old, he naturally looked to Germany, whose methods of research were just coming into vogue at Oxford through the influence of Pattison and Jowett. And since to speculative thinkers of that time German philosophy meant the philosophy of Hegel, Green's fundamental conceptions were derived by Hegelian modes of thinking. In other words, he was a neo-Hegelian. But, as his biographer notes, he never committed himself unreservedly to the Hegelian credo. "While he regarded Hegel's system as the 'last word of philosophy,' he did not occupy himself with the exposition of it, but with the reconsideration of the elements in Kant of which it was the development." That is, he was a neo-Kantian as well as a neo-Hegelian. Of his constructive thinking in these channels the most complete embodiment is his 'Prolegomena to Ethics.'