1. What Are Externalities?

Definitions, classifications, and why they cause market failure

Definition

Externalities are costs or benefits of market transactions that are not reflected in market prices but are borne by third parties (society) who are not directly involved in the transaction as buyers or sellers. (Dr. Said's slides + Dr. Galal)

In Dr. Galal's words: "Externalities refer to the unintended side effects of economic activities - production or consumption - that affect third parties who are not directly involved in the transaction."

Why do externalities matter? Because when costs/benefits spill over to third parties without being priced, the market price sends the wrong signal. Producers and consumers make decisions based on incomplete information (only private costs/benefits), leading to either too much or too little production compared to what society needs.

Classification

Negative Externalities (click)

Costs imposed on 3rd parties. Market overproduces. e.g., Pollution, noise, congestion

Positive Externalities (click)

Benefits to 3rd parties. Market underproduces. e.g., Vaccination, education, R&D

Pecuniary Externalities (click)

(Dr. Said only) Price effects on existing consumers from changes in D/S. Not true market failure.

No Externality (click)

All costs/benefits reflected in prices. Market achieves efficiency on its own. MSB=MPB, MSC=MPC.

Production vs Consumption Externalities

Negative Production

Factory pollution into rivers (paper industry), vehicle emissions, noise from construction

Negative Consumption

Smoking (2nd hand smoke), traffic congestion, noise from neighbors, gambling addiction, litter from tourists

Positive Production

Flood defence projects, deforestation reduction, bee-keeping & pollination, R&D spillovers

Positive Consumption

Vaccination (herd immunity), education, healthcare, pest control, mass transit usage

Why Government Intervention? (From Handwritten Notes)

Three main reasons for government intervention in our society:

  1. If there are positive or negative externalities (production or consumption)
  2. If there is monopolistic power in the market
  3. If there is incomplete information
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