In economics, an externality or external cost is an indirect cost or benefit to an uninvolved third party that arises as an effect of another party's activity. Externalities can be considered as unpriced components that are involved in either consumer or producer market transactions. Air pollution from motor vehicles is one example. The cost of air pollution to society is not paid by either the producers or users of motorized transport to the rest of society. Water pollution from mills and factories is another example. All (water) consumers are made worse off by pollution but are not compensated by the market for this damage. A positive externality is when an individual's consumption in a market increases the well-being of others, but the individual does not charge the third party for the benefit. The third party is essentially getting a free product. An example of this might be the apartment above a bakery receiving some free heat in winter. The people who live in the apartment do not compensate the bakery for this benefit.
Air pollution from motor vehicles is an example of a negative externality. The costs of the air pollution for the rest of society is not compensated for by either the producers or users of motorized transport.
Light pollution is an example of an externality because the consumption of street lighting has an effect on bystanders that is not compensated for by the consumers of the lighting.
Economics is a social science that studies the production, distribution, and consumption of goods and services.
A 1638 painting of a French seaport during the heyday of mercantilism
The publication of Adam Smith's The Wealth of Nations in 1776 is considered to be the first formalisation of economic thought.
The Marxist critique of political economy comes from the work of German philosopher Karl Marx.
John Maynard Keynes was a key theorist in economics.