Computers and robots replace humans in the exercise of mental functions in the same way as mechanical power replaced them in the performance of physical tasks. As time goes on, more and more complex mental functions will be performed by machines. Any worker who now performs his task by following specific instructions can, in principle, be replaced by a machine. This means that the role of humans as the most important factor of production is bound to diminish—in the same way that the role of horses in agricultural production was first diminished and then eliminated by the introduction of tractors.

Leontief (1983) "National perspective: The definition of problem and opportunity", in: National Academies, The Long-term Impact of Technology on Employment and Unemployment: A National Academy of Engineering Symposium, June 30, 1983. p. 3.