All negations don’t sound right to me.

The construction "All X are not Y" should be avoided because the meaning is unclear. Instead, it is better to say "Not all X are Y" or "No X are Y". Then the listener will understand.

In fact, the construction "All X are not Y" is very clear: it means that not one single X is Y. The action is negated for all the subjects.

Just because too many confuse "All X are not Y" and "Not all X are Y" (which negates some - not all - of the of subjects) doesn't mean the construction is unclear. It simply means that people do pay attention to the precision of the syntax.

Oops. What I meant to say is that people don't pay attention to the precision of the syntax.

Obviously, in this case, I didn't pay attention to what I was writing, an oddly ironic lapse in a discussion about negation.

doesn't this popularity of "all X are not Y" meaning "not all X are Y" derive from "all that glitters is not gold"?

As an advertising professional, I see this construction all the time (as your example of the ad copy suggests), and I share your bewilderment. For what it's worth, as it was explained to me when I challenged my copywriters, the first construction "All insurance policies are not the same" takes some liberty to stress the "not" in the sentence. You might (or might not) agree that "Not all insurance policies are the same" seems a bit weaker--especially if you're the one selling them--than "All insurance policies are not the same." Almost by its awkwardness in the middle of the sentence, the "not" calls attention to itself, thereby doing its job as "good ad copy."

As for the second construction, that's just a result of a nitiwtted store manager who flunked 8th grade English. Nowhere have I encountered such grammatical mistakes as in retail shops. Fascinating.

FlapJack, you are wrong. "All X are not Y" is not "very clear". The fact that everyone normally would interpret "All cars are not Ferraris" as "Not all cars are Ferraris", should be enough proof of that. How can you call it very clear when everyone normally interprets it the way you say is wrong? Logically the sentence can have two meanings (I am sure someone more skilled than me in set theory can show this), and since one of them (Not all X) is far more used than the other, that one should be used and not the other, to avoid confusion.

"All that glitter is not gold" is from Shakespeare, so blaming Bush is rather uncalled for.

"Logically the sentence can have two meanings (I am sure someone more skilled than me in set theory can show this),"

In formal logic, "All X are not Y" ALWAYS means "no X are Y", because "not" always modifies whatever it's next to. It is only because people accept the idea that "not" can modify something else that the phrase is interpreted differently.

Sorry UIP, but you're quite wrong. In formal logic, "all X are not Y" does not in fact mean "no X are Y" -- rather, it means "not all X are Y.

A few of you seem to forget that mathematics, specifically, logic and set theory, has an orderly and consistent set of formal rules that apply, well, to mathematics. Language is not mathematics. The structure "all x is not y" simply does not necessarily have the same formal and consistent definition in language as it does in mathematics.

Also, might it not also be possible that "All insurance policies are not the same" in an advertisement is exactly what the advertisers want to say? I would suggest that it's at least possible that they really don't mean "Not all insurance policies are the same" I think they mean exactly that every single insurance policy is different from every other insurance policy. That's part of the message. That's the only way they can claim that theirs is better than every other one. They need you to accept that no other policy can offer what theirs does.

"A few of you seem to forget that mathematics, specifically, logic and set theory, has an orderly and consistent set of formal rules that apply, well, to mathematics. Language is not mathematics."

Amen to that.

Language is logical of course, but in the holistic sense rather than the particular.

That is to say, the logical output of all languages is successful communication and in this they succeed, despite grammatical usages which may not in themselves appear "logical."*

Take the poor old much reviled "double negative" in English. There are those who say this is wrong on the basis of "mathematics": two negatives make a positive so it's logically incorrect, blah, blah.

There are two problems with this approach:

1. Does anyone truly believe that someone who says "I ain't sayin' nothin'" is slyly employing a neat logic trick and really means "I am saying something"?

2. Logic is universal so the laws of logic should apply equally in any language. If the "double negative" is wrong in English grammar on the basis of "logic," should it not be wrong in French as well? And yet, in French, the "double negative" is the standard and it's colloquial to use a "single negative." This is the complete reverse of English usage.

* And anyway, what is "logical" or not at the level of individual grammatical usage is a highly subjective question.

>Sorry UIP, but you're quite wrong. In formal logic,
>"all X are not Y" does not in fact mean "no X are Y"
>-- rather, it means "not all X are Y.

Sorry, amazed, simply asserting something does not make it so. More precisely, the universal quantifier, which is usually expressed as “all”, when preceding a statement about a variable, means that that statement is true for all values that that variable can take. I am confounded as to how you could possibly think that it means "not all X are Y”. In what Math class did you learn that?

>If the "double negative" is wrong in English grammar on
>the basis of "logic," should it not be wrong in French as well?
>And yet, in French, the "double negative" is the standard
>and it's colloquial to use a "single negative."

French doesn’t have a double negative, it has a negative concord. English also has a negative concord. Note the difference between “I saw something” and “I didn’t see anything”. The negation is marked in two places: the contracted “not”, and the switch from “something” to “anything”. Even though the negative is marked in two different places in the sentence, it’s not a double negative. In French, if someone says “Je ne parl pas”, that means “I don’t speak at all”. It does NOT mean “I don’t speak nothing”. Implicit in your argument is that there has to be an exact one-to-one correspondence between words in different languages: for every word in one language, there has to be one, and exactly one, word that means exactly the same thing in the other language. This is ridiculous.

>And anyway, what is "logical" or not at the level of individual
> grammatical usage is a highly subjective question.

Logic is, by definition, not subjective.

"Logic is, by definition, not subjective."

Er, no kidding.

QED.

And by the way, when we say "double negative" we mean only one thing: the use of two negative particles/words together.

Thus, ipso facto, French relies heavily on double negatives just as many English dialects do.

The irony here is that so-called "Standard English" despises double negatives while so-called "Standard French" insists on them.

Et - juste en passant, mon ami, je suis francophone, moi. L'orthographie requise est donc "je ne parle pas" et non "je ne parl pas". En plus, la phrase "je ne parle pas" veut dire (si l'on prend le temps de la traduire littéralement - c'est-à-dire, mot-par-mot - en anglais) "I not speak no(t)."