The late David Mellinkoff, in his much venerated The Language of the Law (Little Brown1963), traces and/or back to scholarly concerns about the correct translation of some famous words in the Magna Carta:
…nisi per legale judicium parium suorum vel per legem terrae.
"Except by lawful judgment of his peers vel by the law of the land."
The debate over the meaning of vel raged. Does it mean and or or?
Mellikoff cites Holdsworth's A History of English Law (1922) among others, noting that the law interpreters agreed on and/or as the best translation. Apparently an ancient Latin division between the copulative and disjunctive was not very meaningful. For centuries the courts have argued about this (Mellikoff, 147-152), often contradicting each other. Several legal scholars have called and/or "a bastard" since the first time it was called into question (1845). Mellinkoff concludes that it has several understandings (307-308):
- It includes every possibility imaginable with and alone plus every possibility imaginable with or alone.
- It should best accord with the equity of the situation.
- It includes some but not all of the possibilities of and and or (but legal scholars disagree about which possibilities to include).
- It means either and or or but it can't mean both.
- It is meaningless.
In his excellent book, The Language of Judges (Chicago 1993) Larry Solan (who is both a linguist and a law professor) devotes 14 pages to "the and/or rule" as it is used in the legal context, noting that commentators on statutes who have encountered the legal uses of and, or, and and/or say that this expression is notoriously loose and inaccurate.
Mellinkoff's understanding 2 seems the best. It would seem that Geoff Pullum is quite right when he says: "The right theory of what or means in English is that it is in general inclusive but that sometimes the exclusive case is conveyed as a conversational implicature."
Maybe some day this will be clear to the field of law.