Growth will slow down when you run out of extra sausagermakers. Unless you learn to make more and better sausages more efficiently, you will suffer the law of diminishing returns. Unless babies are to be drafted into the workforce, that rise is unrepeatable. The most straightforward argument against Mr Krugman is also the hardest to evaluate. Some economists say his numbers are just plain wrong.
Nobody really knows what causes it to grow.
But he argues that it is possible to construct reasonably reliable indices of inputs. Add these up, and you find that inputs have grown no slower than output. TFP, therefore, has not grown at all. Mr Krugman compares such anecdotal argument to the observations of 19th-century Britain by William Cobbett, a radical writer. Cobbett saw continued poverty and missed the industrial revolution.