An attentive reader will easily discover that some of the views expressed in some of the papers are inconsistent with views expressed in others. The fact is that some of the views expressed in some of the earlier ones are views with which I no longer agree; and I feel that some apology is needed for nevertheless republishing them exactly as they stood. In all cases, except one, my excuse is that the mistaken views in question are so embedded in the form and substance of the papers in which they occur, that it would have been impossible to correct them without practically substituting new papers for the old ones; and that, in spite of these mistakes, the old papers, as they stand, still seem to me, on the whole, to say things which are worth saying in a form which, however defective it may be, I doubt my own ability to improve upon. The only case in which I doubt whether this excuse applies is that of the first paper--"The Refutation of Idealism." This paper now appears to me to be very confused, as well as to embody a good many down-right mistakes; so I am doubtful whether I ought to have included it. But in this case I have another excuse: namely that it is a paper to which a good many allusions have been made by contemporary writers on philosophy; and I was told that, for some readers at all events, it would be a convenience that it should be re-printed along with the rest, if only for the sake of reference. I said above that the only one of the previously published papers, in which changes have been made, is IX on "External and Internal Relations." In this case the changes are not due to any change in my views, but to the fact that, in that part of the paper in which symbols are used, I tried, when it was first published in the _Proceedings of the Aristotelian Society,_ to use the symbols adopted by Whitehead and Russell in _Principia Mathematica,_ and used them also without giving an explanation of their meaning which would be sufficient for readers not acquainted with that work. The symbols in question are symbols which it is difficult for printers to reproduce; and I have, therefore, thought it better, on this occasion, to use another set of symbols, which seem to me to be adequate for the limited purpose I had in view. I have tried to give an explanation of their meaning, which will enable anyone to understand them; and I have taken the opportunity of rewriting some of the parts of the paper in which they occur in a way which will, I hope, make some points clearer than they originally were. I have to thank the Committee of the Aristotelian Society for permission to reprint the large number of papers (viz., II, III, V, VI, VII and IX), which originally appeared in the _Proceedings_ of that Society; and the Editor of the _New Quarterly_ for permission to reprint the article on Hume's Philosophy (IV), which appeared in that Journal in November, 1909. G. E. MOORE. CAMBRIDGE, _January_, 1922. Philosophical Studies