Presumption n. a rule of law which permits a court to assume a fact is true until such time as there is a preponderance (greater weight) of evidence which disproves or outweighs (rebuts) the presumption. Each presumption is based upon a particular set of apparent facts paired with established laws, logic, reasoning or individual rights. A presumption is rebuttable in that it can be refuted by factual evidence. One can present facts to persuade the judge that the presumption is not true.