As the phrase has grown in usage in recent years, from business jargon to legal writing and popular culture, it has likewise come under criticism. Some grammarians have pointed out that the phrase is redundant, since the word "or" logically and grammatically encompasses the same meaning. That is, the sentence "Jim will eat cake, pie, or brownies" still permits Jim to eat one, two, or all three of the choices.
Others argue that in a very legalistic society, the word "or" is no longer sufficiently clear, because it may indicate choices that are mutually exclusive (see exclusive disjunction). The word "and" by itself is of no help here, as it requires that all of the conditions are met; in other words, that Jim will eat all three of the choices. Thus, they argue, "and/or" serves the function of clearly indicating that every case is available and that they may be combined.
Such arguments fail to take into account, however, that the word "either" should be used in cases where it is not clear if "or" is designating mutual exclusivity or not. "When using either as a conjunction, you can apply it to more than two elements in a series. Thus, "Jim will eat either cake, pie, or brownies" appropriately indicates that the choices are mutually exclusive. If the function of "or" is clear from the context, it is not necessary to use "either" as a conjunction. Consider the following exchange:
Kim: You may select one item for dessert.
Jim: What are my choices?
Kim: You can eat cake, pie, or brownies.
The phrase has come under considerable criticism in the legal profession in both American and British courts. Judges have called it a "freakish fad," an "accuracy-destroying symbol," and "meaningless." The Wisconsin Supreme Court referred to it as "that befuddling, nameless thing, that Janus-faced verbal monstrosity." Perhaps most crushing of all, the Kentucky Supreme Court said it was a "much-condemned conjunctive-disjunctive crutch of sloppy thinkers." It is particularly damaging in legal writing, in addition to being generally sloppy writing, because a bad faith reader of a contract can pick whichever suits him, the "and" or the "or. Courts called on to interpret it have applied a wide variety of standards, with little agreement.
One may also say, "Jim will eat any of the following: cake, pie, or brownies."
Use of 'and/or' in reference to the payee on a cheque has been contemplated in both the United States and Canada. In the United States, UCC §3-110 - Identification of Person to Whom Instrument is Payable - states that
If an instrument is payable to two or more persons alternatively, it is payable to any of them and may be negotiated, discharged, or enforced by any or all of them in possession of the instrument. If an instrument is payable to two or more persons not alternatively, it is payable to all of them and may be negotiated, discharged, or enforced only by all of them. If an instrument payable to two or more persons is ambiguous as to whether it is payable to the persons alternatively, the instrument is payable to the persons alternatively.The last part reading If an instrument payable to two or more persons is ambiguous as to whether it is payable to the persons alternatively, the instrument is payable to the persons alternatively contemplates use of and/or, and how an item with those words written is to be accepted (use of or prevails).