A Treatise on Probability was published by John Maynard Keynes while at Cambridge University in 1921. The Treatise attacks the classical theory of probability and proposes a "logical-relationist" theory instead. In a 1922 review, Bertrand Russell, the co-author of Principia Mathematica, called it "undoubtedly the most important work on probability that has appeared for a very long time," and a "book as a whole is one which it is impossible to praise too highly." The Treatise is fundamentally philosophical in nature despite extensive mathematical formulations. The Treatise presents an approach to probability that is more subject to variation with evidence than the highly quantified classical version. Keynes's conception of probability is that it is a strictly logical relation between evidence and hypothesis, a degree of partial implication.