Section 67 provides that contents of all documents should be proved by primary evidence. Essentially the law is giving effect to what parties do i.e. to perpetuate the memory of that which they have committed themselves to and also to guard against fraud. The general rule then is that a transaction that has been reduced into writing should be confined to the document and oral evidence should not be allowed for the following reasons:
1. To avoid the use of extrinsic or oral evidence to substitute the terms of the document i.e you want to immortalise what you have agreed to and committed in writing.
2. To guard against the use of oral or extrinsic evidence to contradict, vary, add to or subtract from the contents of the document.
The first concern is the concern to avoid substitution of the document and it is found in Section 97(1) of Evidence Act. The law requires that a matter be reduced into writing or when the parties are in agreement that the matter be reduced into writing. The document becomes the sole memorial of what it is that parties have gotten into.
The rule is qualified by 2 exceptions contained at Section 97(2). The exception are:-
1. Pertaining to Wills – Wills can be proved by probate and the seal which has letters of administration attached to it.
2. Where a public officer is required by law to be appointed by writing if it is shown that a person has been acting as such, then the writing by which he was appointed need not be proved. The reason is to make things workable.
Section 98 is to the effect that when a document has been produced or Secondary Evidence of it given, all oral evidence between the parties to the document is generally inadmissible to contradict, vary or subtract from the contents of such document. The rule would only apply to bilateral agreement and parties to the document. A third party or stranger would not be bound.
There are various qualifications to this rule which are contained as a proviso to Section 98 which is as follows: -
(i) Any fact may be proved which would invalidate any document or which would entitle any person to any decree or order relating thereto; such as fraud, intimidation, illegality, want of due execution, want of capacity in any contracting parties, want or failure of consideration, mistake in fact or law.
(ii) Extrinsic evidence may be tendered to supplement the terms of the document. 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, and in considering whether or not this paragraph of this proviso applies, the court shall have regard to the degree of formality of the document.
(iii) Extrinsic evidence can be brought to prove that parties agreed that a condition would be precedent to the attaching of obligations. Parties may agree but decide that the terms are predicated on certain terms. Oral evidence can be brought in to show the condition precedent.
(iv) Where there is a distinct oral agreement to modify or rescind a transaction which is not required by law to be in writing or which is not registered in conformance with the law, then the oral agreement is to be admitted.
(v) If you get into a transaction that will ordinarily be subject to any usage or customs, then oral evidence of those usages and customs will be admitted.
(vi) Any fact which shows in what manner language used in a document is related to existing facts.