The presumption which the law attaches to certain acts or facts by holding them to be certain exempts the person in whose favour it exists from proving it.
It is said to be simple, when the law reserves proof to the contrary, and may then be rebutted by any means of proof; it is said to be mixed, when the law limits the means by which it may be rebutted or the object on which it may be rebutted; it is said to be irrebuttable when it cannot be rebutted.