We are currently experiencing an outpouring of concern both popular and professional regarding technological unemployment. I shall be discussing an apparent about-turn on the subject by David Ricardo (17721823), who at different times, even in different chapters of the same book, and, indeed, even at different places in the same chapter, seemed to be on both sides of the argument as to whether technological unemployment should be a matter for concern. In a chapter entitled "On Machinery," added to the third edition of his Principles of Political Economy (1821), which comprises volume 1 of his Collected Works (195173), Ricardo announced that he had become concerned about the possibility, even likelihood, of technical change detrimental to labour's interests. However, in the very same "On Machinery" chapter, Ricardo also outlined qualifications to show that there was little need for concern. Ricardo's opposing messages are reflected in contrasting reactions to the chapter "On Machinery." Some readersincluding Thomas Robert Malthus and J. R. McCullochunderstood it as supporting working-class opposition to machinery. Othersincluding John Stuart Mill and Sir John Hicksfind therein the answer to such opposition.