This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Whether a contract may be reformed for mistake in expression when such mistake is apparent from the entire contract and may be corrected by construction,1 is a question upon which the authorities are not unanimous.
Some courts hold that any mistake in expression may be corrected in equity,2 in analogy to a bill quia timet, the question of the absolute necessity of reformation being allowed to affect only costs. So a contract in which by mistake the date for performance is fixed at a time prior to the execution of the contract may be reformed even though the correct date might be inferred by persons familiar with that business.3 Other courts hold that equity 'will not interfere unless the reformation sought will modify the legal effect of the contract,4 on the ground that otherwise plaintiff has an adequate remedy at law. The answer to this may well be that while adequate the remedy may not always be clear.
In any event, if the reformation sought will change the legal effect of the contract, even slightly, it will be given if otherwise proper.5