Where both the parties to an agreement are under a mistake as to a matter of fact essential to the agreement, the agreement is void.
Explanation.—An erroneous opinion as to the value of the thing which forms the subject-matter of the agreement, is not to be deemed a mistake as to a matter of fact.
Illustrations
(a) A agrees to sell to B a specific cargo of goods supposed to be on its way from England to Bombay. It turns out that, before the day of the bargain, the ship conveying the cargo had been cast away and the goods lost. Neither party was aware of the these facts. The agreement is void.
(b) A agrees to buy from B a certain horse. It turns out that the horse was dead at the time of the bargain, though neither party was aware of the fact. The agreement is void.
(c) A, being entitled to an estate for the life of B, agrees to sell it to C. B was dead at the time of the agreement, but both parties were ignorant of the fact. The agreement is void.