Externalities
An externality occurs when an action imposes costs or benefits on people outside a transaction.
The Mechanism: An externality occurs when an economic activity affects third parties who are not fully represented in the transaction. Pollution is a negative externality; vaccination can create benefits for others beyond the person vaccinated.
The Philosophical Pivot: A price can coordinate buyers and sellers while leaving out consequences borne by neighbors, future generations, or shared ecosystems. What appears efficient to participants may be costly to everyone else.
The Horizon: Taxes, subsidies, regulation, and liability can bring some external effects into decision-making. Choosing a remedy requires measuring impacts and deciding how costs should be distributed.
Not every spillover is easy to price, and some values cannot be adequately represented by a fee. The ability to pay is not the same as moral permission to impose harm.
Externalities also reveal that property lines and market boundaries do not match the boundaries of consequences.
A fair system asks not only whether an activity creates value, but who is exposed to its unpriced effects.
A transaction may be private while its consequences are shared.
Which costs of my everyday choices are absent from the price because someone else has been made to absorb them?