Exercise 1: Why the Great Smog Is a Genuine Market Failure — Possible Solution
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A tragic event alone doesn't automatically qualify as a market
failure - a market failure specifically means a real, identifiable
breakdown in how a market's own price mechanism accounts for the true,
full costs (or benefits) involved in a transaction, not just that
something bad happened.

The specific market feature that failed here was the price mechanism's
own inability to make the parties actually causing the pollution (coal
burners - households and industry) pay a price that reflected the real,
full cost of that pollution. The price paid for coal at the time
reflected only the private cost of mining, transporting, and burning
it - it included nothing for the real, genuine harm the resulting smog
imposed on Londoners' own health, since those affected people weren't
parties to any of the coal transactions taking place and had no way to
be compensated or to influence the price through the market itself.

Because the people bearing the real cost (through illness and, per the
modern estimate, an additional 10,000-12,000 deaths) were completely
outside the transactions generating that cost, the market's own price
signal never reflected the true full cost of burning coal - buyers and
sellers of coal kept transacting at a price that was, in a real economic
sense, artificially too low, since it excluded a real cost that fell
entirely on someone else. That gap between the private cost reflected
in the market price and the true, full social cost is exactly what a
negative externality, and therefore a genuine market failure, means.

ANSWER: The specific market feature that failed was the price
mechanism itself - the price of burning coal reflected only its
private cost to buyers and sellers, with no way to include the real
cost imposed on Londoners' health, since those affected people were
outside the coal transactions entirely. That gap between the market
price and the true full cost is what makes the Great Smog a genuine
market failure, not simply a tragic event.

WHY THIS WORKS AS AN ANSWER
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This identifies the specific mechanism (the price signal excluding a
real cost borne by outside parties) that defines a market failure,
rather than treating any bad outcome as automatically qualifying.