In the years after the Great Recession, tens of thousands of Detroit properties were bought by absentee landlords and faceless LLCs. The owners are so negligent and hard to find that the city mows their lawns without asking.

“Blight is rewarded, building is punished,” he said in a recent speech, repeating it over and over for emphasis.

The refrain is a windup for Mr. Duggan’s scheme to fix the blight: a new tax plan that would raise rates on land and lower them on occupied structures. Slap the empty parcels with higher taxes, the argument goes, and their owners will be forced to develop them into something useful. In the meantime, homeowners who actually live in the city will be rewarded with lower bills.

“The phrase we use is ‘Land should eat,’” Mr. Duggan, 65, said in a recent interview at his office.

Georgism gets its name from Henry George, who in the 1890s turned a book, “Progress and Poverty,” into a populist movement. George’s argument was that since land derives most of its worth from its location and the surrounding community, that community, and not the owner, should realize most of the benefits when values rise. His fix might sound wonky — tax the value of land but not improvements atop it — but it made him a celebrity in the 1890s.