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Is using "and/or" allowed in formal writing? If not, is there general way to represent the OR binary operator with as little space as possible in written English?

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Related: Alternatives to “and/or”? –  RegDwigнt Apr 15 '11 at 5:45

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up vote 5 down vote accepted

I believe most style books advise against using and/or in formal writing. By "formal" I mean in newspapers or novels. If space is extremely limited, most writers would have no qualms about it, as in dictionary entries or footnotes.

The reason is that or can mean either "either A and not B, or B and not A" or "A or B or both" in ordinary language: 99 % of the time, readers will be able to figure out whether it is used inclusively or exclusively based on context. If ambiguity could arise, the writer should add some context to make it clear:

This test may be taken on June 5 or July 12.

May the test be taken twice? There are several ways to clarify this, though not every way may work in any situation. Suppose the answer was yes:

This test may be taken on June 5 and July 12 [this may still not be clear in some cases].

This test may be taken twice, on June 5 and July 12.

This test may be taken on June 5, and again on July 12.

This test may be taken on June 5 or July 12, or on both dates.

Suppose the test might be taken only once:

This test may be taken on either June 5 or July 12 [this may still not be clear in some cases].

This test may be taken once, on June 5 or July 12.

This test may be taken on June 5 or July 12, but not on both dates.

Etc.

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In the general English usage, the conjunction 'or' mostly follows the logical meaning of 'exclusive or', that is, it is almost always used in instances where the alternatives cannot take place at the same time. So 'or', even in circumstances where the alternatives are not exclusive, seems to imply that the two alternatives, even if they can, are not to be considered at the same time.

So if you want to express the inclusive or', the possibilities being: {one, the other, both}, you need to add in 'both' somehow. The lengthy way would be to say "A or B or both A and B" or "A or B or both", but an abbreviation is "A and/or B".

And, no, it's not particularly formal; it most likely does not show up in newspapers. I find if you have to translate 'and/or', I find the best is "A or B or both", but I am not a writer, so I'm sure there are better alternatives.

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And/or is, in the vast majority of contexts, redundant. It's a construct that has become lexicalized and has evidently [come under intense criticism][1].

Take the following example

Please mail and/or FAX your reply.

This type of construct is extremely common, but what does this sentence mean? Either I will send my reply by mail, or I will send it by FAX, but I can not do both, so why the "and"?

I suggest using or where there are options from which you should pick only one and simply explain that multiple options are possible from a list when introducing it. As in the preceding sentence, only use and when both apply.

Regarding your specification of "formal writing": if you are writing for a specific audience or body, consult their style manual and employ it as gospel regardless or your (or my) preferences.

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"And/or" in your example would specifically mean that you can "mail", "fax", or "mail and fax". Why would you not be able to do both? "And/or" specifically means "or (not exclusive or)" — it has a meaning that is distinct from simply "or" (formality level notwithstanding). –  Kosmonaut Apr 15 '11 at 0:28
    
@Kosmonaut Indeed, you are correct that it's physically possible to do all three. But that's precisely my point: The implied meaning of and/or is almost never ¬XOR. The writer of the instructions in my example means XOR. –  msanford Apr 15 '11 at 0:33
    
That is strange; I've never seen "and/or" used to mean XOR before. –  Kosmonaut Apr 15 '11 at 0:48

I personally use and/or when it is logically true. In some cases it is important to stress that BOTH options can be done, or a single option can be done (either or both can be done). Although it is often misused in cases where OR is sufficient. Otherwise, the use of OR may exclude BOTH options, when exclusion isn't the intent (that would be an XOR).

'Formal writing' I don't really buy into much. I am always writing formally, unless I'm SMS texting someone maybe. Even if in a research paper, it is fine, unless you have an anal retentive English teacher. In the real world it is accepted and appropriate, I believe. It is clearer than the longer expansion "A or B, or both".

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