One of the fundamental principles of the law of evidence is that in all cases the best evidence should be given. The maxim of law is that whatever is in writing must be proved by the writing. Sec 91 of the Indian Evidence Act, 1872 incorporates this principle. The provision of Sec 91 is further supplemented by Sec 92 by the principle.

Evidence of terms of contract, grants etc., and reduced to document (Section 91):

According to Section 91 of Indian Evidence Act 1872, “when the terms of a contract, grant or some other disposition of property is reduced to the form of a document or is required by law to be reduced to a document, no evidence shall be given for the proof of the terms of such contract etc. except the primary or secondary evidence of the writing itself.”

This Section applies equally to cases in which the contract etc. is contained in one document or more than one. If a contract is contained in several letters, all the letters must be proved (Explanation 1 of Sec 91).

Where there are more originals than one, one original only need be proved (Explanation 2 of Sec 91).

Exclusion of evidence of oral agreement (Section 92):

The provision of Section 91 is further supplemented by Section 92 by providing that once any such contract, grant or disposition has been proved by the writing, then no evidence can be given of any oral agreement to contradict or change the terms of the contract. In other words, no oral evidence can be given to qualify the terms of the document.

Section 92 precludes only the parties to the document and their representatives in interest from giving oral evidence concerning the contents of document. Other parties (or strangers) are left free to give such evidence. Further, evidence can be given of any oral agreement which does not contradict, vary, add or subtract from the term of document.

Roop Kumar v. Mohan Thedani AIR 2003 held that this Section 91 embodies the best evidence rule, thus declaring a doctrine of substantive law. Even a third party, who is seeking to prove a written contract, can prove it only by producing the writing. In this respect Section 91 and Section 92 supplement each other. They are both based on the “best evidence rule” though they differ in some material particulars also.

Exception- When oral evidence can be given regarding a document:

There are various exceptions to the general rule of exclusion of evidence of oral agreement-

~Validity of document (Proviso 1 of Section 92) - The evidence can be given of any fact which would invalidate the document in question or which would entitle a party to any decree or order relating to the document. The validity of a document may be questioned on the grounds of fraud, intimidations, illegality, and failure of consideration, mistake in fact or law.

~Matters on which document is silent ( Proviso 2 of Section 92) - The existence of any separate oral agreement as to any matter on which a document is silent, and which is not inconsistent with its terms, may be proved. In considering whether or not this proviso applies, the Court shall have regard to the degree of formality of the document.

~Condition Precedent (Proviso 3 of Section 92) - The existence of any separate oral agreement, constituting a condition precedent to the attaching of any obligation under any such contract, grant or disposition of property, may be proved.

~Rescission or Modification (Proviso 4 of Section 92) - The existence of any distinct subsequent oral agreement to rescind or modify any such contract, grant or disposition of property, may be proved, except in cases in which such contract, grant or disposition of property is by law required to be in writing, or has been registered according to the law in force for the time being as to the registration of documents.

~Usages or Customs ( Proviso 6 of Section 92)- Any usage or custom by which incidents not expressly mentioned in any contract are usually annexed to contracts of that description, may be proved: Provided that the annexing of such incident would not be repugnant to, or inconsistent with, the express terms of the contract.

~Relation of Language to Facts (Proviso 6 of Section 92) - Any fact may be proved which shows in what manner the language of a document is related to existing facts.

~Appointment of a Public Officer (Exception 1 of Section 91) - When a public officer is required by law to be appointed in writing, and when it is shown that any particular person has acted as such officer, the writing by which he is appointed need not be proved. 

~Will (Exception 1 Section 91) - Wills admitted to probate in India may be proved by the probate.

~Extraneous Facts (Explanation 3 Section 91) - Where in addition to the terms of the contracted a document refers to any other fact also, as to that fact oral evidence is always allowed.