Positive externality

Indian Economy glossary

Also called: External benefit · Topic: Market Structures, Market Failure and Competition · NCERT: Beyond NCERT

Meaning

A positive externality (also called an external benefit) is a benefit that one person's action gives to other people, called third parties, who do not pay for it. The market price ignores this benefit, so the free market produces too little of the good compared with the social optimum (the best level for society as a whole). This makes it a type of market failure (a case where the free market, left alone, gives a wasteful result).

Formula: Social benefit = Private benefit + External benefit

Explanation

How it works

  • Private benefit is the gain to the person who buys or does the thing. For example, a vaccinated person is protected from disease.
  • External benefit is the gain to others who are not part of the deal. For example, the neighbours of that person face a lower risk of infection.
  • Social benefit = Private benefit + External benefit. When there is a positive externality, social benefit is greater than private benefit.
  • Why too little is produced:
  • The buyer compares only their own benefit with the price.
  • The buyer ignores the gain to others, because nobody pays them for it.

  • So some units that society would want are never bought, and output is too low.

  • Root cause: a missing market. There is no place where the neighbours can pay you for their lower infection risk. With no price, the benefit is not counted.

Worked example: a vaccine dose (numbers are for illustration only)

  • One vaccine dose costs ₹400.
  • The person who takes it gains ₹300. This is the private benefit.
  • Their neighbours gain ₹200 because their risk of infection falls. This is the external benefit.
  • Social benefit = 300 + 200 = ₹500. This is more than the ₹400 cost, so society wants the dose taken.
  • The person's decision:
  • they compare only ₹300 with ₹400;
  • the cost is higher than their own gain, so they refuse the dose;
  • so the market ends up with too little vaccination.

Common examples

  • Vaccination leads to herd immunity. When enough people are vaccinated, the disease cannot spread easily. Even people who are not vaccinated are protected.
  • Education gives society citizens who are more productive and better informed.
  • R&D (research and development) creates knowledge that other firms can copy and build on.

Remedies: how to raise output to the optimum

  • Pigouvian subsidy. This is a payment for an activity with a positive externality, equal to the external benefit. The idea comes from A.C. Pigou, The Economics of Welfare (1920).
  • In the example, a ₹200 subsidy brings the person's cost down to ₹200.
  • ₹200 is below their ₹300 private benefit, so they now take the dose.

  • This "internalises" the externality. That means the person's own sums now include the benefit to others.

  • Direct provision by the state. Free vaccines are an example.

  • Why private bargaining (the Coase theorem) usually fails here:
  • In theory, the neighbours could pay the person to get vaccinated.
  • In practice, there are too many neighbours, so bargaining is very costly.
  • Each neighbour also hopes the others will pay. This is free riding.
  • So very little money is collected, and the state has to act.

In India

  • Free vaccines. The government pays the full cost of the dose. This protects both the person vaccinated and the wider community through herd immunity.
  • FAME / PM E-DRIVE. The government helps people buy electric vehicles. EVs mean less tailpipe pollution, which benefits everyone who breathes the air, so this is a Pigouvian subsidy.
  • PM Surya Ghar. The government subsidises rooftop solar. Clean power benefits people well beyond the household that installs the panels.
  • Crop residue management. The government subsidises machines that manage crop leftovers. This rewards farmers for not burning stubble.
  • Stubble burning is a negative externality: the smoke drifts to Delhi and makes its winter air worse.

  • Paying farmers to use the machines is a Pigouvian subsidy for a cleaner choice.

  • Education and R&D. The state funds schools and research because society gains more from them than the individuals who pay for them.

Don't confuse with

  • Negative externality. It is a spillover cost, not a benefit. Because social cost is greater than private cost, the market overproduces. With a positive externality, it underproduces.
  • Pigouvian tax vs Pigouvian subsidy. A tax equal to the marginal external cost (the extra harm to others from one more unit) is used on harmful goods, such as tobacco. A subsidy equal to the external benefit is used on goods with a positive externality, such as vaccines.
  • Public good. A public good such as clean air is non-excludable, meaning no one can be stopped from enjoying it. A good with a positive externality can still be sold to one buyer. A vaccine dose goes to one person, but part of its benefit spills over to others.
  • Private benefit. This is only the buyer's own gain. Social benefit adds the external benefit on top. The market responds only to private benefit.

Prelims Hooks

  • Social benefit = Private benefit + External benefit. With a positive externality, social benefit > private benefit, so the market gives too little output.
  • Correct remedy: a Pigouvian subsidy equal to the external benefit. It comes from A.C. Pigou, The Economics of Welfare (1920).
  • Pairs to remember:
  • vaccination → positive externality (herd immunity);
  • stubble burning → negative externality;
  • PM Surya Ghar or PM E-DRIVE → Pigouvian subsidy;

  • tobacco tax → Pigouvian tax.

  • Trap: a positive externality causes underproduction, not overproduction. Both kinds of externality are market failures.

  • Classic examples: vaccination, education and R&D. Knowledge from R&D spreads to other firms that did not pay for it.
  • Coase theorem ("The Problem of Social Cost", 1960; Coase won the Nobel in 1991) [1][2]. It says clear property rights and low transaction costs lead to an efficient bargain. For external benefits spread across many people, bargaining costs are high, so it rarely works.

Mains Points

  • Why the state pays for health and education (GS-III and GS-II):
  • people weigh only their own gain from vaccination or schooling;
  • so, left to the market, society gets too little of both;

  • this is why free vaccination, public schooling and public R&D funding are justified, and it is not only a welfare argument.

  • Subsidy design matters:

  • a Pigouvian subsidy works only when it roughly matches the external benefit;
  • too small, and output stays too low; too large, and public money is wasted;

  • the same applies to schemes such as FAME / PM E-DRIVE and PM Surya Ghar.

  • Rewarding good choices, not just punishing bad ones:

  • subsidising machines for crop leftovers turns stubble management into a positive-externality activity;
  • this shows that subsidies and penalties can work together where private bargaining fails;
  • it fails here because there are too many parties, rights are unclear and bargaining costs are high.

Related concepts

Read more

Sources

  1. 1Ronald Coase — Britannica Moneybritannica.com · tier 3
  2. 2The Problem of Social Cost — Britannicabritannica.com · tier 3