两术语均是指陪审团就法庭所列举的事实进行的推定。mandatory presumption (也称为 absolute presumption；conclusive presumption；irrebuttable presumption；presumption juris et de jure) 为“必然性推定”，指法律规定陪审团必须就特定事实为基础的 证据作出的推定(a presumption that a jury is required by law to make upon proof of a given fact)。而 permissive presumption 则为“随意性推定”，指陪审团可以作出的但非法律所规定必须就某特定事实所作出的推定，其也称为permissive inference (随意性推论）[2]。

[1] Cf. Linda Picard Wood, J. D. , Merriam Webster's Dictionary of Law, at p. 379, Merriam -Webster，Incorporated (1996 ).

[2] “A presumption that a trier of fact is free to accept or reject from a given set of facts. ”Cf. Bryan A. Gamer, Black's Law Dictionary, 7th edition, at p. 1204, West Group (1999).