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How does negation affect the use and understanding of “or” and “and”

If I want to negate a sentence such as

I like beer and whiskey. [Most commonly understood as, I think, I like beer and I like whiskey.]

I have to convert the and to an or:

I don't like beer or whiskey.

There's no sense of an or in the second sentence, so its inclusion seems a bit perverse. I realise that I could say

I don't like beer and whiskey.

but that would mean something different:

I don't like (beer and whiskey).

rather than the intended

(I don't like beer) and (I don't like whiskey).

So my question is: what's going on here? Why do we have to make this change?

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    A formal statement of the way this works is De Morgan's Laws in Boolean algebra: en.wikipedia.org/wiki/De_Morgan's_laws
    – bye
    Jul 22, 2011 at 9:36
  • isn't it supposed to use 'nor' like I don't like beer nor whiskey
    – Sufendy
    Jul 22, 2011 at 9:40
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    @Phelios You are thinking of "I like neither beer nor whiskey."
    – z7sg Ѫ
    Jul 22, 2011 at 10:27
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    Technically correct but practically unused is 'I like beer nor whiskey', meaning I don't like either.
    – Tim Lymington
    Jul 22, 2011 at 11:37
  • Not yet pointed out: "Beer and whiskey" might be some kind of combination, which you're either liking or not liking all-together-in-one-glass. "Or" makes it clear that you're talking about two separate things; "And" is ambiguous.
    – buildsucceeded
    Jul 22, 2011 at 16:25

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I don't think it's as clear cut as you make out. If I wanted to know if you liked those two drinks, I might ask 'Do you like beer or whiskey?' And you could say 'I don't like beer and whisky' and be understood. Both conjunctions can be used; context will determine their meaning.

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And/or is part of the general discussion, called Boolean operations. On the base ground of your own reasoning, we can also interpret

I like bear and whiskey

as

I like (bear and whiskey)

in which bear and whiskey is interpreted as a combination, not as different individual things.

It's more like saying

I like coffee and sugar.

In this statement, the listener/reader doesn't interpret coffee and sugar as two different things. Though when we want to denote the combination, we usually use with, like saying

I like coffee with sugar

but still using and makes us interpret the two things as a combination (This was all based on your own reasoning for negative interpretation).

So, what happens here is that the listener either interprets the phrase as a combination of two things, or two individual things and the and/or doesn't make this interpretation. I believe that it's the context which differentiates the interpretations.

Thus, all of the sentences you mentioned are valid enough to be perceived as either one of the interpretations, and nothing magical happens here.

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    What are all those bears doing with the whiskey, hey?
    – Daniel
    Jul 22, 2011 at 16:23
  • The bear will steal your whiskey.
    – apaderno
    Jul 23, 2011 at 18:25

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