What does a point on the PPC represent?
A point on the production possibilities curve represents productive efficiency: the economy is using all of its resources fully with its current technology, so it cannot produce more of one good without producing less of the other. Any move along the curve has an opportunity cost.
A production possibilities curve puts one good on each axis and traces the most of one good the economy can make for each amount of the other. A point on the curve is one of those maximum combinations. Producing there means the economy has no idle workers beyond normal job turnover, no unused factories, and resources assigned so that no reshuffling could produce more of one good without less of the other. That condition is productive efficiency, and every point on the curve has it.
Take an economy that produces robots (horizontal axis) and corn (vertical axis), with these points on its curve: 0 robots and 100 corn, 10 robots and 90 corn, 20 robots and 70 corn, 30 robots and 40 corn, and 40 robots and 0 corn. Suppose it produces at 20 robots and 70 corn. That point is on the curve, so the economy is getting the most corn possible given that it makes 20 robots.
Producing on the curve also means every change has a price. To go from 20 robots to 30 robots, the economy must move down the curve to 40 corn, giving up 30 corn for 10 robots, an opportunity cost of 3 corn per robot. To go the other way, from 20 robots and 70 corn to 10 robots and 90 corn, it gains 20 corn and gives up 10 robots, an opportunity cost of 0.5 robots per unit of corn. This is what students mean when they say that on the curve there is a trade-off: more of one good always means less of the other.
Compare the other two cases on the same graph. The point 20 robots and 50 corn is inside the curve, since the curve allows 70 corn at 20 robots; the economy could get 20 more corn without giving up any robots, because resources sit idle. The point inside the PPC answer covers that case in full. The point 30 robots and 70 corn is outside the curve, since the curve allows only 40 corn at 30 robots, so it is unattainable with current resources and technology.
Being on the curve does not tell you which point is best. All points on the curve are productively efficient, but only one is allocatively efficient: the mix of robots and corn that matches what society values most. A point with 40 robots and no corn is on the curve, yet a society that needs food would not choose it. The PPC explainer walks through all the points on one graph, and the PPC sandbox lets you drag a point along, inside, and outside the curve.
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Related questions
- Are all points on the PPC equally good?
- They are equally efficient in production, since each one uses every resource fully. They are not equally desirable. Which point is best depends on what society wants, and only the point that matches those preferences is allocatively efficient.
- What does a point to the right of the PPC mean, and why?
- A point to the right of, or outside, the curve is unattainable right now, because producing it would take more resources or better technology than the economy has. It becomes reachable only if the curve shifts outward through economic growth. Through trade, a country can [consume beyond its PPC](/answers/can-a-country-consume-beyond-its-ppc), but it still cannot produce there.
- Does a point on the PPC mean there is zero unemployment?
- No. A point on the curve means full employment, which in economics still allows normal frictional and structural unemployment as people change jobs. It rules out the extra cyclical unemployment of a recession, which would put the economy inside the curve.