The downward (negative) slope of the production possibility frontier represents which economic principle?

The downward (negative) slope of the production possibility frontier (PPF) illustrates the concept of opportunity cost. As production shifts from one good to another, the resources must be reallocated, which often leads to a decrease in the quantity of the good being forgone. The curve illustrates that to produce more of one good, the economy must reduce the production of another good, indicating that there is a trade-off involved.

This trade-off demonstrates that resources are limited and cannot be used simultaneously for the production of both goods. The steeper the slope at any given point on the PPF, the higher the opportunity cost of producing one good over the other, highlighting the fundamental economic principle that choices must be made due to scarcity. The downward slope effectively communicates the idea that as you produce more of one good, you give up quantities of another, which is the essence of opportunity cost in economics.