The interpretation of the writings of Ludwig Wittgenstein has occupied many philosophers for some decades and will doubtless occupy many more for further decades. This is in part due to the fecundity of his thought, to its ability to shed light on so many problems of philosophy and on different aspects of particular problems. But there are other reasons too.
First, while his style, both in the Tractatus and in his quite different later writings, is simple and powerful, it makes scant concessions to his readers. As he remarked in the Preface to the Investigations, it was not part of his purpose 'to spare other people the trouble of thinking'. He had a craving for the erlösende Wort, the redeeming word that would unlock a philosophical problem, go to the heart of a conceptual difficulty, and show how the knotted threads of our understanding are to be disentangled. Having found a form of expression that achieves that, he was loath to spell out the detailed implications that ensue—preferring to retain the power of concisely expressed insight rather than to water it down with what evidently appeared to him pedestrain elaboration. This makes formidable demands upon his readers. That is one reason why the surviving Nachlass is an indispensable tool for the interpretation of his thought. For there one can often find the dozens of pages of struggle that lead up to, and shed light on, the one or two sentences constituting the remark that is the final expression of his thought on the matter.
Secondly, Wittgenstein is unique in the history of philosophy in having produced two powerful complete philosophical world-pictures crystallized respectively in the Tractatus and the Investigations. How precisely these stand to each other, how much continuity and how much change there are between the two philosophies, will very likely be a perennial source of controversy, as one reader observing, as it were, the bridges between two land masses will note the connections between them, while another will be overwhelmingly impressed by the gulf that separates them.
Thirdly, each of his great masterpieces presents profound difficulties of interpretation quite apart from their forms of expression and compression. The Tractatus cannot be understood without familiarity with the works of Frege and Russell, to which it is a critical, and indeed