41. Equitable rules.

41.     Equitable rules.

In equity, oral evidence is admissible to make out a case for rectification or rescission of an instrument1, or to show that what purports to be an agreement is not in fact an agreement at all, for example, where it has been signed by mistake2. In such cases the evidence is admissible, not to contradict what appears on the face of the agreement (which the court will not allow), but to prove the existence of a mistake which could not otherwise be proved3. Similarly, where mistake cannot be established without