Presumption, in law, an inference or assumption made in the absence of evidence. Presumptions are divisible into conclusive presumptions and disputable presumptions. Conclusive presumptions answer to the prcesumptio juris et de jure of the civil law. The law asserts them to be true, and will not permit evidence to deny or refute them. A familiar illustration may be found in the rule that a debt which has run 20 years, whether under seal, or by judgment, or resting on other evidence, is conclusively presumed to have been paid. If it be sued one day before the 20 years expire, the creditor need only prove the debt, and the debtor must prove that he has in some way satisfied it. But if it be sued one day later, not only is the debtor relieved from the necessity of proving payment, but the creditor will not be permitted to prove that the debt has not been paid. If the creditor can prove anything which the law would recognize as a new promise within 20 years, the suit may be maintained on this new promise, but the old debt is conclusively settled.

Another common instance is the rule in respect to land, possession of which under a claim of absolute ownership for a certain period constitutes a conclusive presumption of a valid grant, which cannot be disturbed by evidence. (See Limitation, Statutes of, and Prescription.) - Conclusive presumptions are not very common in the law; but disputable or rebuttable presumptions, answering to the prcesumptio juris of the civil law, constantly occur. They are indeed little more than legal inferences from existing evidence, open to modification or reversal by further evidence. They are much the same with prima facie conclusions or inferences; as, for example, when one sues on a promissory note, and proves his own possession and the signature of the maker, the law presumes the plaintiff to be the owner of the note, and also presumes consideration, and gives the plaintiff his case, unless the defendant overcomes the presumption by evidence on his part of some ground of defence. The general presumptions of innocence in favor of an alleged criminal, and of absence of debt in favor of a defendant in a civil suit, are of this kind.

It will be seen therefore that disputable presumptions do little more than determine where the burden of proof rests.