Born and educated in Cambridge, Johnson’s main livelihood was teaching mathematics, until he was made a Fellow of King’s College, Cambridge, in 1902. He had considerable personal and intellectual influence on the younger Cambridge generation that included Broad, Keynes, and the empiricist and philosopher of probability, R. B. Braithwaite. His own major work, Logic, was collected in three volumes in the last decade of his life, but has not achieved a large subsequent impact.