What is meant by ‘May Presume’, ‘Shall Presume’ and ‘Conclusive proof’?

What is meant by ‘May Presume’, ‘Shall Presume’ and ‘Conclusive proof’?

The presumption has an important place in evidence law. 
According to the evidence act we need evidence in court to prove the fact. But, sometimes there are few such facts which are deemed to be proved on the grounds of presumption. 

Section 4 May presume

Whenever it is provided by this Act that the Court may presume a fact, it may either regard such fact as proved, unless and until it is disproved or may call for proof of it.
A court has the discretion to presume a fact as proved or to call for confirmatory evidence as the circumstances require. In such cases, the presumption is not a hard and fast rule. The presumption is Juris et de jure. The court is free to presume any fact or not as the presumptions are about the question of facts. It may regard such fact as proved, unless and until it is disproved or may call for the proof of it.
If in a case the court has an option to raise the presumption and raises the presumption, the distinction between two categories of presumptions ceases and the fact is presumed, unless and until it is disproved. It is open to the Court upon proof of a marriage on a certain date, either to regard as proved the subsistence of the marriage on a subsequent date unless and until it should be disproved or else to call for proof of it.
Example – When a man has not been heard for seven years by those who would have naturally heard of him if he had been alive, his death shall be presumed. Such death is called “Civil Death’ 

Shall presume

Whenever it is directed by this Act that the Court shall presume a fact, it shall regard such fact as proved, unless and until it is disproved.
The court is bound to presume a fact as proved. The presumption is an irrebuttable presumption as it is the presumption of law. Whenever there is a provision to the effect, “that the court shall presume a fact,” the court cannot exercise its discretion, but in such circumstances, the court shall have the liberty to allow the opposite party to adduce evidence to disprove the fact so presumed. If the party is successful in disproving it the court shall not presume the fact. 

Example:
Under section 89 of the Evidence Act, “the court shall presume that every document, called for and not produced after notice to produce attested, stamped and executed in the manner required by law.”

“Conclusive proof”:

When one fact is declared by this Act to be conclusive proof of another, the Court shall, on proof of the one fact, regard the other as proved, and shall not allow evidence to be given for the purpose of disproving it.
Section 112 of the Indian Evidence Act, 1872 is a good example of conclusive proof. It has been said in the section 112 that – “The fact that any person was born during the continuance of a valid marriage between his mother and any man, or within 280 days after its dissolution, the mother remaining unmarried shall be conclusive proof that he is the legitimate son of that man unless it can be shown that the parties to the marriage had no access to each other at any time when he could have been begotten” 

Comments:

When a fact is a ‘conclusive proof’ of another fact the court has no discretion to disprove it. It is irrebuttable presumption and the court shall not allow evidence to be given for the purpose of disproving it. “Conclusive proof’ gives an artificial probative effect by the law to certain facts. No evidence is allowed to be produced with a view to combating that effect. In this sense, it is an irrebuttable presumption. “Conclusive proof: is also within the realm of the Evidence Act. Where a statute makes certain facts as final and conclusive, evidence to disprove such facts is not to be allowed. This is the strongest of all presumptions. When any person signs a document is presumed that he has read the document properly and understood it and only then he has affixed his signature thereon, otherwise, no signature on a document can ever be accepted. “In particular, businessman, seeing careful people (since their money is involved) would have ordinarily read and understood a document before signing it. Hence the presumption would be even stranger in their case.”

Example:
Birth during marriage, a final judgment of the court, or a degree conferred by the University.