Philosopher. His first book, Language, Truth, and Logic, written when he was only twenty-six, became widely influential. In it, he valued empiricism and logic to the complete exclusion, indeed the derision, of alternative mental modes such as emotion or intuition. In addition, certain past applications of logic, notably metaphysics, were deemed to be illogical nonsense, a position that had already been articulated by David Hume more than a century earlier. Ayer later softened but did not abandon his position, which was often referred to as Logical Positivism.