George Edward "G. E." Moore OM, FBA was an English philosopher, one of the founders of the analytic tradition along with Bertrand Russell, Ludwig Wittgenstein, and (before them) Gottlob Frege. With Russell, he led the turn away from idealism in British philosophy, and became well known for his advocacy of common sense concepts, his contributions to ethics, epistemology, and metaphysics, and "his exceptional personality and moral character." He was Professor of Philosophy at the University of Cambridge, highly influential among (though not a member of) the Bloomsbury Group, and the editor of the influential journal Mind. He was elected a fellow of the British Academy in 1918. He was a member of the Cambridge Apostles, the intellectual secret society, from 1894, and the Cambridge University Moral Sciences Club.
These are papers written by Moore between 1897 and 1903, beginning when he was in his mid-twenties. They strongly reflect the Cambridge of his time, especially the influence of Kantian idealism and J. M. E. McTaggart's interpretation of Hegelian idealism.
I think it would be an exaggeration to say that these papers represent a distinctive "early Moore" analogous to the "early Wittgenstein" -- they are very much early flexings, I think, for his more mature thought in Principia Ethica (1903, actually at the same time as some of the later papers here) and the "common sense philosophy" (1925 and later) he is better known for. Unlike in those later works, Moore doesn't so much stake out strong positions of his own here as criticize and defend those of others.
The philosophical structures and vocabulary he works within here are drawn from Kantian and Hegelian influences. It's a little odd, for someone who has read Moore's well-known works, to read his discussions of McTaggart, Lotze, and others who stand solidly in that tradition of German idealism. To read Moore discuss "the Absolute" or what "in and for itself" might mean has a surreal feel.
But it's not hard to find continuities between these writings and Moore's later thought. In particular, Moore's style and method -- his thorough analytic approach -- are on full display. The combination of that approach with the idealism of McTaggart (especially in his paper on "McTaggart's `Studies in Hegelian Cosmology'") is exactly the kind of monumental collision you might think it would be -- Moore's unwavering insistence on conceptual clarity bashing up against McTaggart's embracing of broken distinctions and apparent contradictions.
Moore also presages a theme from Principia Ethica with an attack on moral naturalism in his essay on "The Value of Religion". And he scathingly and even sarcastically attacks McTaggart's idealism, including a very Moore-like remark:
"The history of philosophy exhibits a uniform inability to distinguish between that of which I am conscious and my consciousness of it -- an inability which has found a monument in the word `idea' which regularly stands for both."
All in all, as a fan of Moore's better known works, I found my impression of Moore as a philosopher more completely filled out by these papers. I certainly wouldn't begin reading Moore by starting here -- the papers don't really stand on their own -- what makes them interesting is exactly in supplying a more complete picture of Moore's development.