Language Reports

And/or: The Janus-Faced Conjunction?

June 2019

And/or is a common term in written English, particularly in legal, technical and journalistic texts. It is also widely criticized: the Chicago Manuel of Style warns writers to “Avoid this Janus-faced term.” Meanwhile, it has been described in courts of law as a “grammatical monstrosity”, a “bastard conjunction”, and worse. So why is and/or so controversial? And how did the term come about in the first place?

The History of And/or

Legal scholar David Mellinkoff suggests that and/or was originally coined in order to avoid a translation problem. The Magna Carta, written in medieval Latin, contained several instances of the word vel, which may be translated as and or or, depending on the context. However, in some cases, the meaning was ambiguous and subject to extensive debate. The solution, at least for some interpreters of the law, was and/or. By joining these two conjunctions with a forward slash, they allowed it to be interpreted as one or the other. In other words, and/or means “and or or”.

The expression caught on, and was common in legal and mercantile documents by the late 19th century. It then spread to other technical domains before entering general usage by the late 20th century. It may seem surprising that this obscure legal conjunction could have come into such widespread use, particularly given its unusual form: its forward slash renders it both aesthetically displeasing and difficult to pronounce—should you simply ignore the slash and say “and or”, or is “and slash or” preferable?

Inclusive Or Vs. Exclusive Or

The popularity of and/or is rooted in the fact that the word or may be interpreted as inclusive or exclusive. Inclusive or means that, in a phrase consisting of multiple elements joined by the conjunction or, the inclusion of one of these elements does not necessarily entail the exclusion of the others. Take the following example:

“We are looking to hire someone with knowledge of Spanish or Portuguese”

Naturally, a person who knows Spanish but not Portuguese would fit the bill, as would someone who knows Portuguese but not Spanish. What about a person who knows both Spanish and Portuguese? Does the fact that they know both languages exclude them from the running? The answer, of course, is no. Someone who knows both languages may also apply for the position. The or in this example is inclusive, meaning that it allows for the inclusion of one or more of the items in question.

However, or is not always interpreted in this way. Take the following example:

“Our brunch menu includes a free tea or coffee.”

In this case, a customer may order tea with their brunch for no extra charge. Alternatively, they may order coffee. But can a customer order both tea and coffee and expect to pay no extra? The answer is no. The or in this example is intepreted as exclusive, meaning that it allows for the inclusion of one, and only one, of the items in question.

Since and/or means “and or or”, its meaning is identical to that of the inclusive or. As the above examples illustrate, the question of whether or is inclusive or exclusive is usually easy to discern by considering the context. It would be entirely unnecessary to use and/or in the first example, since it is obvious that the this or is inclusive. So why did people use and/or?

Occasionally, context is not enough. Moving on to the second example, imagine an unusually generous restaurant that allows its customers to choose both tea and coffee at no extra charge when they order brunch. Since the or in the example would be considered exclusive, it is not sufficient to communicate the restaurant’s offer. Replacing or with and would also be unsatisfactory; it would imply that both tea and coffee are served with brunch and customers have no choice in the matter. So and/or is a quick solution to the problem of the out-of-context inclusive “or”:

“Our brunch menu includes a free tea and/or coffee.”

The Case Against And/or

And/or may not be the most attractive of terms, but as we have seen, it is not entirely useless. Why, then, are so many authorities so fiercely against it? Does it really deserve to be called “Janus-faced” by a style guide?

Critics of and/or see it as a careless shortcut taken by writers who are unable or unwilling to choose between and and or. They maintain that or is usually an adequate replacement which would cause no change in meaning, because, they say, or should always be interpreted as inclusive unless the context dictates otherwise. Indeed, and/or is largely overused, and or does suffice in most cases. What’s more, in logic and computer science, the operator “or” is inclusive, which supports the idea that and/or is redundant.

However, we know that language does not always follow the rules of logic. As the example of the generous restaurant illustrates, we may sometimes need to specify that an or is inclusive. For such occasions, the Chicago Manual of Style’s proposed solution is to add “or both”, as in the following sentence:

“Our brunch menu includes a free tea, or coffee, or both.”

Other critics suggest that, if the inclusiveness of the word or is ambiguous, it would probably be better to reformulate the text entirely.


And/or can be a convenient solution for a specific problem, but it presents several problems of its own. The forward slash, aside from rendering and/or difficult to pronounce, may also result in confusion since it is a symbol with multiple different uses. Additionally, a quick internet search for “and/or” reveals that it is widely overused and mostly replaceable with a simple or. For those exceptional circumstances in which an or really is ambiguous, a reformulation in the manner suggested by the Chicago Manual is usually the best option.

Still, and/or probably doesn’t deserve all of the vitriol it receives. Contrary to what some critics say, it does have a purpose, although its execution is far from ideal. Some writers may still choose to use it for the sake of brevity, although they should limit this to contexts in which a brief style is acceptable, and unlikely to provoke the ire of copy editors.