The three kinds of operative mistake are:

• Common Mistake: In common mistake, both parties make the same mistake. Each knows the intention of the other and accepts it, but each is mistaken about some underlying and fundamental fact. For example, the parties might be unaware that the subject matter of their contract has already perished.
• Mutual Mistake: In mutual mistake, the parties misunderstand each other and are at cross-purposes. For example, A intends to offer his Nissan Sunny car for sale, but B believes that the offer relates to Nissan Corona, also owned by A.
• Unilateral Mistake: In unilateral mistake, only one of the parties is mistaken. The other knows, or must be taken to know, of his mistake. For instance, A agrees to buy from B a specific painting which A believes to be genuinely that of painter Offei, but which in fact is not but a copy from Appia. If B is ignorant of A’s erroneous belief, the case is one of mutual mistake, but if he knows of it, it is a case of unilateral mistake.

(1.667 marks each = 5 marks)