Mr. Greenleaf, Sec. 14, divides presumptive evidence into two branches: "Presumptions of law" and "Presumptions of fact." "Presumptions of law," says Mr. Greenleaf, "consists of those rules, which, in certain cases, either forbid or dispense with any ulterior inquiry." They are founded either upon the first principles of justice, or the laws of nature; or the experienced course of human conduct and affairs, and the connection usually found to exist between certain things. The deliberate firing of a deadly weapon presumes a malicious intent to kill or do bodily injury, and twenty years of open and notorious, distinct and exclusive, hostile and adverse possession of land presupposes a prior lost grant. Absence unheard from for seven years or more presupposes the death of the person.

Presumptions of law have been divided into two classes, conclusive and rebuttable presumptions. Conclusive presumptions lose the character of presumptions and become absolute and fixed rules of law declaring a particular fact to be true under particular circumstances and forbidding any inquiry into its truth or falsity. Rebuttable or disputable presumptions may be overcome by countervailing evidence.

It appears that presumptions of law either assert that when a certain fact or series of facts exists, a certain other fact is deemed to be established either conclusively or until disproved by other evidence; while a presumption of fact is only a conclusion or inference which a judge or jury is at liberty to adopt or to reject as it sees fit. Other authors have added to the above classes, natural and artificial presumptions, weak presumptions, and strong or violent presumptions, until the whole subject of presumptions involves the mind in inextricable confusion.