In contract law a mistake
is incorrect understanding by one or more parties
to a contract and may be used as grounds to
invalidate the agreement. Common law has
identified three different types of mistake in
contract: unilateral mistake, mutual
mistake, and common mistake.
Unilateral
mistake
A unilateral mistake is where only one party to a
contract is mistaken as to the terms or
subject-matter. The courts will uphold such a
contract unless it was determined that the
non-mistaken party was aware of the mistake and
tried to take advantage of the mistake.
The leading case on unilateral mistake is Smith
v. Hughes (1871).
Mistake of identity
It is also possible for a contract to be voidable
if there was a mistake in the identity of the
contracting party. In the leading English case of
Lewis v Avery [1971] 3 All ER 907 Lord Denning
held that the contract can only be avoided if the
plaintiff can show, that at the time of
agreement, the plaintiff believed the other
party's identity was of vital importance. A mere
mistaken belief as to the credibility of the
other party is not sufficient.
Mutual
mistake
A mutual mistake is when both parties of a
contract are mistaken as to the terms. Each
believe they are contracting to something
different. The court usually tries to uphold such
a mistake if a reasonable interpretation of the
terms can be found.
The famous case of the Peerless ship is an
example in the case of Raffles v. Wichelhaus,
(1864) 2 Hurl. & C. 906. The defendant had
made an order for the purchase of cotton for
goods arriving on a certain boat Peerless from
Bombay leaving in October. However a different
boat arrived called Peerless, also from Bombay,
but having left in December. The plaintiff
merchant sought to enforce the contract for the
sale of cotton, but the defendant refused stating
that it was not the cotton that he had ordered.
The court stated that reasonable meaning must be
found. However, on the facts, there was no single
reasonable interpretation of the terms, both
parties were equally mistaken, thus the contract
was void.
Common
mistake
A common mistake is where both parties hold the
same mistaken belief of the facts.
The House of Lords case of Bell v. Lever Brothers
Ltd. established that common mistake can only
void a contract if the mistake of the
subject-matter was sufficiently fundamental to
render its identity different from what was
contracted, making the performance of the
contract impossible.
Later in Solle v. Butcher, Lord Denning added
requirements for common mistake in equity, which
loosened the requirements to show common mistake.
However, since that time the case has been
heavily criticized in cases such as Great Peace.
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