What is an externality?

A cost or benefit affecting someone who was not a party to the transaction that created it.

Why do externalities cause market failure?

Because the price does not reflect the full social cost or benefit, so too much of a harmful activity and too little of a beneficial one is produced.

Externality

noun (countable/uncountable)

/ˌɛkstəˈnælɪti/

A cost or benefit experienced by a third party not directly involved in an economic transaction, which is not reflected in the market price of the good or service; a form of market failure. Negative externalities (e.g., industrial pollution, carbon emissions) lead to overproduction relative to the social optimum; positive externalities (e.g., vaccination, education) lead to underproduction. In India, Pigouvian taxes — such as the National Clean Energy Cess (now GST Compensation Cess on coal) and Green Tax on old vehicles — are instruments to internalise negative externalities.

✍️ Usage in a UPSC answer

India's coal cess, levied since 2010 and restructured under the GST compensation framework, is a textbook Pigouvian instrument designed to make thermal power producers internalise the negative externalities of carbon emissions and local air pollution.

Synonyms

spillover effectthird-party effectsocial cost/benefitside effectneighbourhood effect

Antonyms

private costinternal costno spillovermarket-internalised effect

🌱 Word Family

external (adjective), externalise (verb), internalise (verb, antonymic action), externalities (plural noun), Pigouvian tax (related noun phrase)

🔡 Root

Latin externus = outside, external + -ality = quality noun suffix

📜 Etymology

From Latin externus (outward, foreign), from exter (outside). The economic concept was formalised by A.C. Pigou in The Economics of Welfare (1920), where he distinguished 'marginal social net product' from 'marginal private net product' to capture third-party effects. The noun 'externality' was popularised in post-war microeconomics and public finance literature.

🧠 Memory Hook

EXTERN-ALITY — the word EXTERN means OUTSIDE. An externality is a cost or benefit that FALLS OUTSIDE the private deal, landing on innocent bystanders. A factory's smoke drifts OUTSIDE its walls onto your lungs.

🎯 How This Word Works in UPSC Writing

A cost or benefit falling on someone who is not party to the transaction that produced it. It is the foundational concept for environmental economics in GS3 because it explains market failure precisely: a polluting producer does not bear the health cost imposed downstream, so the market price understates the true social cost and too much is produced. The instruments follow directly, whether taxation, tradable permits or regulation, and all aim at internalising the external cost.

⚖️ Don’t Confuse It With

A negative externality imposes uncompensated costs on third parties; a positive externality confers uncompensated benefits, as with vaccination. Internalising means making the actor bear the cost, typically through a tax or a price. A public good is a distinct category defined by non-rivalry and non-excludability, though the two often appear together.

🇮🇳 Hindi Meaning

बाह्यता (bāhyatā); ऋणात्मक बाह्यता is a negative externality.

❓ Common Questions

What is an externality?: A cost or benefit affecting someone who was not a party to the transaction that created it.
Why do externalities cause market failure?: Because the price does not reflect the full social cost or benefit, so too much of a harmful activity and too little of a beneficial one is produced.

💰 Indian Economy 📖 Seen in: Indian Economy — Growth, Planning & De...

Relevant across:GS3 · Economy, Environment, S&T & Security

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