21. Mistakes as to quality relieving from liability.

There are a few cases where the parties will be relieved from performance because of their mistake as to quality1. The difficulty is to determine whether the mistake goes to the substance of the whole consideration2.

In one case a purchaser agreed to buy an estate which, unknown to him, already belonged to him; as neither party was obliged to perform in those circumstances, the purchaser could recover back the price paid3. Again, where a finance company accepted an offer to buy a car on hire-purchase which, unknown to the parties, had by then been stolen and severely damaged, neither