When I used to teach Legal Research and Writing, one of the phrases I encouraged my students to avoid was "and/or." Like a lot of legalese, I think lawyers believe that using "and/or" leads to greater clarity in their writing when in fact the opposite is true. I suspect that, like much of what I taught them, my students avoided "and/or" in the writing they submitted to me and then quickly went back to using it as soon as they got out of my class. They may have thought that my opposition to "and/or" — like my opposition to "any and all," "heretofore," and any number of other phrases — was personal preference not generally accepted advice. If they did, however, they would have been wrong, and the Appellate Division has now confirmed as much.
In State v. Gonzalez, the Appellate Division reversed defendant's conviction and ordered a new trial because the trial court's repeated use of "and/or" in its jury charges rendered the instructions "hopelessly ambiguous and erroneous in important respects." In that case, defendant was convicted of, among other things, robbery and aggravated assault. (The emphasis on "and" will become clear later.) He was accused of conspiring with two other individuals to rob and then assault another individual. As might be expected, the prosecution and defense presented different versions of the underlying events to the jury. The problem for the Appellate Division was not the evidence that each side presented, but rather the repeated use of "and/or" by the trial judge when he instructed the jury on how to evaluate that evidence.
The Appellate Division began by observing that "[t]he imprecision of the phrase 'and/or' and criticism for its use [in New Jersey] and in other jurisdictions has been well documented." New Jersey's highest court previously described it as an expression that "has never been accredited in this state as good pleading or proper to form part of a judgment record." Courts in other states were less kind, calling it: a "verbal monstrosity, neither word nor phrase;" "an inexcusable barbarism" that was "sired by indolence;" a "mongrel expression" that was "an equivocal connective, being neither positively conjunctive nor positively disjunctive;" and an "abominable invention." The Appellate Division further observed that "[w]henever found in the decisions of [New Jersey] courts, 'and/or' has been recognized as creating ambiguity."
The same was true in Gonzalez, where the Appellate Division held that it was impossible to determine whether "with each utterance of 'and/or,' the jury was able to properly interpret it as 'and' when the judge should have said 'and,' and 'or' when the judge should have said 'or.'" For the Appellate Division, the most troubling impact of this ambiguity was the "possibility that the verdict was the product of less than unanimous findings by the jury." The Appellate Division described this concern as follows:
[T]he nature of the indictment required that the jury decide whether defendant conspired in or was an accomplice in the  commission of a robbery, or  an aggravated assault, or  both. By joining (or disjoining) those considerations with "and/or" the judge conveyed to the jury that it could find defendant guilty of either substantive offense – which is accurate – but left open the possibility that some jurors could have have found defendant conspired in or was an accomplice in the robbery but not the assault, while other jurors could have found he conspired in or was an accomplice in the assault but not the robbery. In short, these instructions did not necessarily require that the jury unanimously conclude that defendant conspired to commit or was an accomplice in the same crime. Such a verdict cannot stand.
This same concern about confusion and ambiguity can arise outside of the criminal context. In fact, when it described the general rejection of "and/or" by New Jersey courts, the Appellate Division cited civil lawsuits involving the use of the expression in insurance policies and wills — Howell v. Ohio Cas. Ins. Co. (finding ambiguity in an insurance policy describing the insured as "husband and/or wife"), and In re Estate of Massey (finding ambiguity in a will bequeathing one-third of the residue to decedent's "niece and/or grandniece"). Therefore, like I told my students all those years go, the bottom line is: avoid "and/or" at all costs. Instead of writing or saying "A and/or B," write or say "A, B, or both." It express the same sentiment, without the same possibility for ambiguity and/or confusion.