Why are "and/or" constructions in English not considered grammatically correct? Consider, for example, the following sentences:

  • "Multi-organ failure can be attributed to confusion, fatigue, and/or delirium not attributable to any other cause."
  • "Multi-organ failure can be attributed to either confusion, fatigue, delirium, or all of them, not attributable to any other cause."

Also, suggest any other way to avoid/reword such constructions.

  • 1
    Who told you and/or isn't grammatically correct? It's in the OED, for one thing. – Dan Bron Jun 30 '15 at 13:15
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    Like many judgments about "correct", this is a purely social judgment, not a linguistic one. Somebody has arbitrarily decided that the word "and/or" is "not proper English", and been able to persuade others to agree. Like wearing the wrong clothes or using the wrong fork, people who believe in "correct" will judge you if you use it. – Colin Fine Jun 30 '15 at 13:30
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    The and/or statement is ambiguous and imprecise. Don't worry about whether it's grammatical. In prescriptive contexts, you should use either precisely as well, with two choices. X can be caused by any of the following: a, b,c, or d; it can also be caused by e and f in combination. – TRomano Jun 30 '15 at 13:39
  • Additionally in a mathematical way "or" contains "and". So one would not have to put both, just the "or" would be sufficient. The one without the "and" would be the "either ... or". Even though most people tend to use an "or" like the "either ... or" version in my experience. – Daniel Jun 30 '15 at 14:49
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    @Tim: Either does not mean and/or. "For dessert, choose either chocolate mousse or cheesecake." "For dessert, choose chocolate mousse and/or cheesecake." If you were a glutton, which choice would you like to have? – Peter Shor Jun 30 '15 at 14:56

Wikipedia’s article on “and/or” summarizes and cites both criticisms and defenses of the expression. Among those cited as condemning it are Strunk & White’s Elements of Style, Fowler’s Modern English Usage (2nd ed., ed. Ernest Gowers), and the current (16th) edition of The Chicago Manual of Style—influential authorities all. Though many hereabouts consider the influence of the first two especially to be pernicious, it suffices to occasion considerable anxiety in some who are tempted to use “and/or”—so that I think is the answer to your headline question. The thing is widely considered ungrammatical (or otherwise to be shunned) because these books say it is.

The common suggestion of those first two controversial authorities is to replace “A and/or B” with “A or B or both.” As to rewording your sentences on multi-organ failure, though, I cannot help you, because I cannot understand either one of them. In particular, I need help understanding how the phrase “not attributable to other causes” relates to what precedes it. Is the diagnostician, pathologist, or etiologist to consider any one or combination of “confusion, fatigue, delirium” as the phenomenon’s cause only if it cannot be attributed to other causes, or what?


It's true that some authorities disapprove of and/or, though I don't believe they go so far as to say the usage is "grammatically incorrect."

As far as I can tell, many of the individuals who don't like this contruction incorrectly believe that the full range of meanings can be covered with "and" or "or" alone, and that there is therefore never any reason to use "and/or."

As your question implies, this isn't true. "A and B", "A and/or B" and "A or B" each have distinct meanings. (These are discussed in detail in response to other questions, and since you seem to understand the distinction, I'm not going to repeat it here.)

Some of those who don't like "and/or" seem to be focused on the fact that, formally, "A or B" is true if A is true, or if B is true, or if both A and B are true. From this, they draw the (incorrect) conclusion that the "and" in and/or is always superfluous.

That said, it does seem to me that "and/or" is overused. One common case is when "A and/or B" is used as a condition for some action. In this case, "A and/or B" can often be replaced by "A or B," and probably should be. (By condition, I mean something like a logical test that will determine if a certain action will/should be taken or result will ensue. I'd welcome a better way of formulating this.)

Example: "Don't turn right if the light is red or if pedestrians are present." Replacing the "or" in the previous sentence with and/or isn't logically incorrect, but it is unnecessary and may be taken as evidence that the speaker didn't bother to think through what he meant to say.

Similarly, I suspect that and/or is often used unnecessarily when describing cause or effect. "X is caused by A, B or C" does not imply that X couldn't be caused by A and C, A and B, or all three. The reason to write X is caused by A, B and/or C is to emphasize the possibility of multiple causes.

Your examples may be a case of using "and/or" unnecessarily when "or" would do. To the extent I understand the meaning you are trying to convey, it does not seem that there would have been any ambiguity if you replaced "confusion, fatigue, and/or delirium" with "confusion, fatigue, or delirium." Since these generally aren't considered to be mutually exclusive possibilities, I don't think that any meaning would have been lost.

On the other hand, the following strikes me as a good use-case for and/or: "Each child standing in line was given a hot dog and/or a hamburger." This because "Each child standing in line was given a hot dog or a hamburger" might very well be read as meaning "a hot dog or a hamburger, but not both."

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