Moore is best known today for his defence of ethical non-naturalism, his emphasis on common sense in philosophical method, and the paradox that bears his name. He was admired by and influential among other philosophers, and also by the Bloomsbury Group, but is (unlike his colleague and admirer Russell, who, for some years thought he fulfilled his "ideal of genius") mostly unknown today outside of academic philosophy. Moore's essays are known for their clear, circumspect writing style and his methodical and patient approach to philosophical problems. He was critical of modern philosophy for its lack of progress, which he believed was in stark contrast to the dramatic advances in the natural sciences since the Renaissance. Among Moore's most famous works are his book "Principia Ethica", and his essays, "The Refutation of Idealism", "A Defence of Common Sense", and "A Proof of the External World".