THE EXCLUSION OF ORAL BY DOCUMENTARY EVIDENCE

Reference: The Indian Evidence Act

Sections 91 to 100 are based upon the principle that the best evidence must always be given, and the acceptance of the fact that no matter how good a person’s memory may be, the best evidence of the content of a document is the document itself.
The principle does not demand the largest amount of evidence – it simply requires the best evidence and since this is documentary evidence, oral evidence is excluded. However, it was held in Javarasetty v. Ningamma, 1992, that oral evidence is not excluded when the writing in question is not evidence of the matter reduced to writing; there is no reason for the Court to prefer either documentary or oral evidence to the other.
The general rule excluding oral evidence in the presence of documentary evidence is laid down in Sections 91 and 92. The general rule is subject to the ‘exceptions’ contained in Sections 93 to 100 which speak of how oral evidence may be used to interpret documents.

Also see:
Section 91: http://indialegal.blogspot.com/2008/04/evidence-of-terms-of-contracts-grants.html
Section 92: http://indialegal.blogspot.com/2008/04/exclusion-of-evidence-of-oral-agreement.html