A plague called The Black Death swept Medieval Europe. At the time, people believed cats spread the plague (cats were associated with the Devil) and started killing them to prevent the spread of disease. In reality, rats spread the plague and the slaughter of their natural predators only hastened the disease's proliferation. With this in mind, a market for cats would have had a ______ externality because the cats ______.
A) positive; prevented rats from eating their owners' grain
B) positive; killed rats regardless of who those rats would infect
C) negative; spread disease to everyone regardless of who owned them
D) negative; made everyone sicker through their association with the Devil

Question

Quizplus · Accepted Answer

A market for cats would have a positive externality because they killed rats regardless of who those rats would infect. This would have helped prevent the spread of disease and ultimately decrease the overall impact of the plague.

A Plague Called the Black Death Swept Medieval Europe