Ernest Nagel (November 16, 1901 – September 20, 1985) was an American philosopher of science. Along with Rudolf Carnap, Hans Reichenbach, and Carl Hempel, he is sometimes seen as one of the major figures of the logical positivist movement.
His work concerned the philosophy of mathematical fields such as geometry and probability, quantum mechanics, and the status of reductive and inductive theories of science. His 1961 masterpiece, The Structure of Science, practically inaugurated the field of analytic philosophy of science. He expounded the different kinds of explanation in different fields, and was sceptical about attempts to unify the nature of scientific laws or explanations. He was the first to propose that by positing analytic equivalencies (or "bridge laws") between the terms of different sciences, one could eliminate all ontological commitments except those required by the most basic science. He also upheld the view that social sciences are scientific, and should adopt the same standards as natural sciences.
Nagel wrote An Introduction to Logic and the Scientific Method with Morris Raphael Cohen, his CCNY teacher in 1934. In 1958, he published with James R. Newman Gödel's proof, a short book explicating Gödel's incompleteness theorems to those not well trained in mathematical logic. He edited the Journal of Philosophy (1939–1956) and the Journal of Symbolic Logic (1940-1946).