Clark and I are moving toward agreement on the implications of the Malthusian model, but I'm still not satisfied. He writes:
Caplan replaces my figure 2.1 with one where disease and harvest failures cause the technology schedule to move down but leave the death rate unchanged. But even if he is correct that bad stuff killed people but also affected production possibilities, then the new picture should still involve a shift in the death schedule.
Does it? It depends. If bad stuff kills people solely by reducing income, then the Technology Schedule should shift, and the Death Schedule should stay fixed. If bad stuff kills people directly, with no indirect effect on income, then the Technology Schedule should stay fixed, and the Death Schedule should go up. If bad stuff kills both directly and indirectly, then both should shift (as I explained in the post script of "Malthus on Stilts").
I'll defer to Clark historical expertise when he describes the Plague as a pure shift in the Death Schedule. But at the other extreme, harvest failures, which Clark praises in identical terms, are basically pure shifts in the Technology Schedule.
The normative statement: - “England was lucky to have been struck by the plague” is more debatable. But let me make that case. 1.5 million people died prematurely in 1349. In return 6 generations got to live very well with little further excess deaths. And then 1.5 million people got to live longer as the plague weakened its grip in the 16th century, and the population returned to its earlier level. The unlucky generation of 1349 was counterbalanced by the lucky generations of 1540-1620.
God smiled on the English when he delivered the plague!
Somehow I doubt that the grief felt by plague survivors at the loss of a third of their families compares to the satisfaction generated by the rising life expectancy of the generations of 1540-1620. But even leaving this aside, I'm puzzled. If we're doing a utilitarian calculus, why isn't it bad to have six generations of lower population?
Question for Clark: What, in your view, is the socially optimal fraction of the population for the plague to kill? If 25% death is a gift of God, why not 50%? 90%?