I’m flummoxed when I see come across the phrase “and/or”. What exactly does it mean when someone says “you can have lunch and/or dinner”? According to the Wikipedia entry, that would mean that you can choose among three possibilities: only lunch, only dinner, or both. It’s that last choice which makes it different from saying “you can have lunch or dinner”, which would mean that you could have either lunch or dinner, but not both. Most definitions of “and/or” leave out the fourth possibility: have neither lunch nor dinner.
In the lingo of Boolean arithmetic, the English word “or” corresponds to the boolean “exclusive or” (xor).
What does the truth table for “and/or” look like?
A B A and/or B true false true false true true true true true false false false
In other words, the phrase “and/or” corresponds exactly to the boolean sense of the English word “or”. Unfortunately, the English word “or” is already used for the boolean xor.
What logical operator does the “/” stand for?
But what logical operation does the “/” stand for? Let’s see:
A B A or B A and B A and/or B (A or B) or (A and B) true false true false true true false true true false true true true true true true true true false false false false false false
This shows us that (at least for the cases we care about), the “/” in “and/or” is equivalent to the boolean or.
Which brings me to the root of my dislike for “and/or”. In the other common use of “/” in the language — in constructions such as “singer/songwriter, "actor/director” — the “/” means and. When we say someone is a “singer/songwriter” we mean that they are a singer and a songwriter. The connotation of “/” in “and/or” is completely different from that.
In any case, I think that “and/or” always leaves room for confusion and uncertainty, and should be substituted with the slightly more verbose but much clearer “you can have lunch, or dinner, or both.”