"All x are not y" - what does this mean to you??

In this post Fuzzy Wombats is talking about whether a group of Iraqis are armed or not.

The phrase used is “Now, from my viewing of that video, I can clearly see weapons. All of them are not armed, but there are a few.

That phrase “All of them are not armed” seems to mean the exact opposite to what is meant?

As a Brit I take “All of them are not armed” to mean “None of them is armed”, which doesn’t appear to be the intention behind it. In fact it’s the complete opposite - i.e. some of them are indeed armed.

Likewise I’ve also seen a similar phrase used in defence of the catholic clergy: “All priests are not abusers”, which surely means “There are zero priests who are abusers” which is not the intention either.

In each case I would have used “Not all of them are armed”, and “Not all priests are abusers”.

So is this just a case of sloppy writing by Fuzzy Wombats, or have I got my grammar confused? :confused:

Thank you-- I’d been hearing that syntax in TV commercials for ages (“All fluoride toothpastes are not alike!”) and it drives me crazy. Too bad they don’t teach basic logic until the college level, and even then I doubt more than a few people even study it a little bit, or we wouldn’t have this syntactical embarrassment.

You’re right, of course, and I’ve been hearing it too . . . along with the use of “less” when they mean “fewer.” You’d think that professional journalists would have a grasp of the English language.

Sloppy writing. I’ve seen similar variances in meaning and resultant confusion with respect to the particular placement of “only,” as well.

Is this an American thing (like “I could care less”), or is it standard english outside the UK?

It’s got nothing to do with logic (and translating English into a formal language, or back again, is fraught with all sorts of difficulties). It’s just proof that the semantics of English aren’t really compositional, and the meaning of one sentence can change depending on its context. Taken in context, it’s easy to see what the sentence means. Even the OP had to focus on a fragment of a sentence to get a contradiction, the second half of the sentence clears up the meaning.

I agree that from context it’s possible to work it out, but that’s making the reader work harder than required, hence my feeling that’s it’s lazy writing.

My first instinct was to parse it as {If X, then ~Y}. Of course, I’ve been teaching formal logic to kiddos lately and the text we use is quite careful to differentiate “All X are not Y” from “Not all X are Y <=> Some X are not Y”.

Those sentences don’t sound right to me either, but at least they have a respectable precedent in “All that glitters is not gold”. What’s really been grating me recently is the use of “anymore” to mean “these days”. I just always have to re-read the sentence to understand it. I seem to almost exclusively see it used here, but that’s probably just because it’s the main place I see informal US English.

wayward, I think what’s been cropping up all over the place is a misspelling: people apparently don’t know the difference between “anymore” and “any more”.
As for the sentence in the OP, I do tend to parse it as the speakers intended. I see “all bananas are fruits, but not all fruits are bananas” and “all bananas are fruits, but all fruits are not bananas” as equivalent, although I’d be more likely to use the first construction.

I understood it right off the bat. Not from any sort of logic, but just because I’ve seen that construction so often that I barely notice it any more.

No, it’s a regionalism and “supposed to” be written that way. We have several dopers here from the area of the US that uses it. Drives me batty as well, but not as much as [object] needs [past tense verb].

I’m wondering now if leaving out the word “not” in phrases the OP mentioned is a regionalism too. I haven’t heard anyone phrase things like that outside a logic class, anyway.

We’ve covered this. “Less” is perfectly fine when used to mean “lower quantity of”, according to any online dictionary that I’ve looked at.

Funny, when I saw the thread title “All x are not y” I thought it meant that some y that are x, but not all of them. When I read the sentence in question, half way through I interpreted it to mean they’re all unarmed, but upon reading the whole thing, I see he meant some are.

When I read, “All X are not Y,” I think it should mean “Every single X is not Y.” “There is no X which is Y.” “The set of X is disjoint from the set of Y.”

However, I am aware that many people use this construction to mean “Not all X are Y.”

So, in practice I treat the phrase as ambiguous and hope I can figure out from the context which they mean.

Maybe it’s regional, but I’ve never encountered anyone using it to mean ‘no x are y’. In my experience, it’s strictly ‘not all x are y’, so that’s immediately how I interpret it.

But that’s what it “should” mean. A statement that begins “All X are…” logically ought to say something about all X. “All of them have beards” would be a statement about all of them; analogously, “All of them are not armed” ought to be a statement about all of them.

Man, you said everything I was going to say. Now what am I going to do?..

(That having been said, I often mentally stumble when confronted with this phrasing as well. C’est la vie.)

I started a thread asking this a while back and I think it was resolved that it’s an English thing that has fallen more quickly out of common use in the UK than in the US. Consider: 'All that glisters is not gold (Shakespeare) and ‘All is not lost’ (Milton)

ETA: Outside of well-established examples such as the above, I often have problems parsing it properly.

I disagree. If you want to say that none of them are armed (or, if you insist, is armed), the usual way to say it is just that, “none of them is/are armed”. Nobody would say “all of them are not armed” to convey that idea, regardless of logic, so I don’t think it does need context to clarify it. It just needs familiarity with common usage.