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I was recently given a specific short sentence, and a question about the conjunction. The sentence was given orally, and I think that's relevant. The sentence is:

  • I don't know how to read and write.

This could mean, I don't know how to read, and I don't know how to write (the intended meaning). It could also mean, I know how to read and I know how to write, but I don't know how to do both at the same time.

To avoid this confusion, I suggested: I don't know how to read or write. Orally, the stress would be on the 'or'.

I'd like to know whether you agree or disagree with this, or am I simply compounding the problem. Many thanks.

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    Note that there is a negative in this sentence. That changes things. Try it first with I know how to read and write. Any problems? Nobody would think to use or in that sentence. And the reason why it pops up in the negative is that negation changes the relation of and and or in certain cases (but not others; it's rather complex). The rules in question are theorems of logic called De Morgan's Laws.
    – John Lawler
    Commented Apr 28, 2021 at 22:33
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    "I don't know how to read and write" is something of an idiom, implying that you are generally illiterate. This classification would tend to apply even if you are part way through the first grade and know the basics of reading and writing -- you're just not proficient.
    – Hot Licks
    Commented Apr 29, 2021 at 0:03
  • There's a negative don't governing everything. That means that negation and conjunction come together, and that means that DeMorgan's Law holds. This flips around AND and OR with the negative. So Not (p and q) is equivalent to Not p or Not q.
    – John Lawler
    Commented Oct 16, 2023 at 22:48
  • @JohnLawler in this case it's not (p or q) is equivalent to (not p and not q): I can't (read or write) means (I can't read and I can't write). But we should be careful about the overzealous application of formal logic to grammatical conjunctions. For example, "nor" functions rather differently: "can't read nor write" means the same as "can't read or write." And most other permutations of logical operators don't yield a different meaning; they rather yield nonsense. For example, if someone "can't read and can write" we don't say that they "can't (read or not write)."
    – phoog
    Commented Feb 14 at 15:46

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The issue with this particular pair of words isn't primarily which conjunction is used, but that "read and write" is something akin to a merism for literacy. The following sentence illustrates this:

Knowing how to "read and write" references the mechanical acts of reading and of writing, but it also goes beyond the mechanics and into the realm of understanding - the ability to understand and to express concepts that are relayed through words.

So saying that someone doesn't know how to "read and write" is saying that they are illiterate, whereas saying that someone doesn't know how to "read or write" speaks more to the mechanical processes, though one might argue that the difference in intent is so slight as to be splitting hairs.

To the broader point of your question - the conjunctions and and or in conversation don't always reduce to what one might expect if using pure Boolean logic. They are sometimes interchangeable and sometimes even conventionally reversed. Context and convention are both needed for disambiguation.

For example:

  • "I don't want fish and chips." Taken as a statement of Boolean logic, serving one without the other would not contradict the assertion. But here, the whole genre of food is rejected; battered fish wouldn't be acceptable even if chips were withheld.
  • "You can have beef or chicken." Boolean logic would allow one to claim both beef and chicken. However, the intent is an exclusive-or: one can claim either protein but not both.
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    And we'd say 'fish and chips is on the menu', emphasising the composite nature of the meal [fish and chips].
    – Edwin Ashworth
    Commented Feb 13 at 23:29
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    For the benefit of the chemists and biologists who are scratching their heads - rhetorical merism - thoughtco.com/merism-rhetoric-term-1691307
    – Phil Sweet
    Commented Feb 14 at 2:24
  • @PhilSweet Thanks. Merism is a good example of when the whole conjunction needs to be taken as-is and not split up. "Read and write" scrapes in as a merism, but "fish and chips" doesn't; it's just (functionally) a compound word.
    – Lawrence
    Commented Feb 29 at 8:40
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I would certainly say "I don't know how to read or write Arabic" because I don't know any words in Arabic and can't form any of the letters. This is the idiomatic way of saying that somone is illiterate in a given language. Someone who is not literate in any language would say "I don't know how to read or write".

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This question is artificial: (i) It presents a false dichotomy - there are better alternatives (ii) the problem is not "and/or", it is your expecting a particular construction that is devoid of context to give good results for different cases, and (iii) it ignores the use of tone in the voice.

You are never going to say "I don't know how to read and write" without context.

  • Look at the page and read it and, as you are reading it, write down any adverb that you see.

  • I don't know how to read and write. (and is emphasised.

In reality, this meaning is so rare that the native speaker would say "I don't know how to read and write at the same time."

Or

  • Read the contract and, at the bottom, write your name and the date.

  • I don't know how to read and write. (and is not emphasised.)

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