Pigouvian Tax, explained.
A Pigouvian tax aims to align private incentives with external marginal costs under suitable information and market assumptions.
Why it happens
Inverse demand is 100−Q, private marginal cost 20 and external marginal damage 20. A tax t implies Q=max(0,80−t). Social surplus is 60Q−Q²/2; tax receipts tQ are transfers rather than resource losses. The optimum in this model is Q=60 at t=20.
A Pigouvian tax aims to align private incentives with external marginal costs under suitable information and market assumptions.
Read the result
Treat receipts as transfers while counting actual external damage. The welfare peak follows marginal costs, not the highest tax revenue.
A worked example
Pricing a twenty-unit external cost
At tax zero, quantity is eighty and social welfare is sixteen hundred under the displayed demand and cost functions.
Set the tax to twenty, reducing quantity to sixty and increasing social welfare to eighteen hundred.
Raise it further and inspect how extra reduction can sacrifice benefits worth more than the avoided costs under this model.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Inverse demand is 100−Q, private marginal cost 20 and external marginal damage 20. A tax t implies Q=max(0,80−t). Social surplus is 60Q−Q²/2; tax receipts tQ are transfers rather than resource losses. The optimum in this model is Q=60 at t=20.
Where this idea is useful
A practical use
A price can omit costs imposed on people outside a transaction, leading to excessive activity under the model's welfare criterion.
A common misconception
“Any tax increase improves an externality problem.”
The appropriate comparison is marginal social benefit and cost, with administrative and distributional consequences considered. Excessive taxes can also create losses.
What this explanation leaves out
- Damage, demand and cost are certain authored functions. Administrative costs, distribution, uncertainty and other distortions are absent. This demonstrates marginal-cost alignment rather than prescribing an actual environmental tax.
Why not subtract tax revenue from social welfare?
The payment moves resources between parties in this model rather than destroying them. Administrative costs or other real burdens would need to be modelled explicitly.
Which marginal external cost would need evidence before choosing an actual corrective price?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.