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I've always understood that you can order the words not and every (or similar words) in the following two ways to convey distinct logical meanings.

  • Every human is not a man. There is no human being who is a man.
  • Not every human is a man. There are human beings who are not men.

Being a non-native speaker, I learn most of my English by reading things on the internet. The thing is that I almost never see people doing it this way and this made me question my understanding.

For example, a comment on another Stack Exchange website reads:

Everything on DOS is not plain-text!

To my understanding, this sentence means that there is nothing on DOS that is plain-text, but it is clear to me that the author of the message intended a different meaning. I would correct this sentence to:

Not everything on DOS is plain-text!

Am I correct and is this mistake very commonly made or do I have a fundamental misunderstanding of this sentence structure?

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Neither. It is a case where English has its rules of interpretation which are not amenable to logic analysis. Every human is not a man is grammatical, and certainly could be interpreted the way tou suggest; but it is something which a native English speakers is extremely unlikely to say, because traditional sentences like all that glisters is not gold render it ambiguous. –  Colin Fine Jul 21 '13 at 20:35
    
Related question: "everything is not ..." –  Peter Shor Jul 22 '13 at 12:10
    
"I learn most of my English by reading things on the internet." Big mistake! Most people writing on the 'net use sloppy English, out of haste, out of ignorance of the rules of the language, or because they just don't care to put in the effort to do it correctly. Don't think that just because it's in writing that it's a good example to learn from! –  Phil Perry Mar 14 at 16:10
    
@PhilPerry When I say that, I don't mean I learn it from YouTube comments and the like, but rather programming articles or news articles. –  Overv Mar 14 at 16:12
    
Even "articles", whether in the general press or technical press, are often poorly written (and a poor example to learn from). I suspect that the hurry to get the articles online contributes to this, not giving time for careful and thoughtful editing. The sheer number of "publishers" probably spreads too thinly those who are good at writing or editing. –  Phil Perry Mar 14 at 16:29

3 Answers 3

up vote 7 down vote accepted

You are correct; Karan of the superuser question you referenced made a grammatical error. It should have been as you phrased it:

Not everything in DOS is plain-text

That being said, your understanding in the two examples you posted is slightly off. It should be

Every human is not a man. There is no human being who is a man.

Not every human is a man. There are human beings who are not men.

Such logic mistakes (especially with double negatives) are very common even among native English speakers. The fact that you are able to discern the intended meaning of Karan's comment, even with its incorrect phrasing, and your excellent grammar in this post tells me that you do not at all have a fundamental misunderstanding; on the contrary, your english seems quite good.

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Thank you. The confusion in the first sentence only proves that it's sometimes difficult to get it right! –  Overv Jul 21 '13 at 17:37
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Please note that, while your logic is correct, it is quite common to find the ‘wrong’ variants in this construction. One need look no further than Shakespeare to find such illogical wordings as, “All that glisters is not gold”. –  Janus Bahs Jacquet Jul 21 '13 at 17:54
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I'm sorry, but this answer is simply wrong. English is English, not logic. I puzzled over every ... is not as a child, before I learned that logic has nothing to do with it. I choose to avoid using sentences of that form, but as @JanusBahsJacquet says, English speakers and writers have done so for centuries. –  Colin Fine Jul 21 '13 at 20:31
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@ColinFine, I wouldn’t say there’s any part of the answer that is wrong per se, except the term ‘grammatical error’ (‘stylistic faux pas’ would have been better). Languages are basically logical in nature, though they sometimes depart from that logic, and it is perfectly permissible and plausible to use the every X is not Y turn of phrase logically (“Every ale in the house is not enough to quench my thirst!”), so avoiding ambiguous uses of it is never a bad idea, as long as you are also aware that not everyone will follow your example. –  Janus Bahs Jacquet Jul 21 '13 at 20:37
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As for the examples, whenever there is more than one Operator (Modal, Negative, Quantifier) in a clause, there is inevitable ambiguity, since each kind of operator binds some constituent, and the fields can twist into some strange configurations. –  John Lawler Jul 21 '13 at 22:36

I am sorry, there seems to be some confusion here. Your understanding of the following sentence seems slightly out of place:

Everything on DOS is not plain-text!

or as it stands corrected

Everything in DOS is not plain-text!

This does NOT mean that everything on DOS is not of the type "plain-text" (whatever that means). What this actually implies is that there might be some things in DOS that are of the type "plain-text" but not every one of them.

Generally, Everthing ... is not.. ... is inter-changable with Not everything is... However, there might be a few exceptions to that.

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To be clear, it is usually interchangeable only because it is so commonly used incorrectly. Everything in DOS is not plain-text does mean that nothing in DOS is plain text if taken only by its logic. –  XenElement Jul 22 '13 at 1:59

Your understanding appears basically correct. Also, the kinds of mistakes you have pointed out are indeed quite common.

Note, however, that the second part of the following item is not equivalent to the first part. (I've starred the second part to indicate its incorrectness as a translation of the first part.) The first part does not imply that humans exist; instead, it implies that if they do, then some of them are not men. The second part unconditionally asserts that human beings exist who are not men, a quite different statement.

Not every human is a man. *There are human beings who are not men.

Edit: The error of equating the two parts is an example of an existential fallacy, and if there were no humans, it would be an example of a vacuous truth. The wikipedia article about existential fallacies says

The existential fallacy, or existential instantiation, is a formal fallacy. In the existential fallacy, we presuppose that a class has members when we are not supposed to do so; that is, when we should not assume existential import.

One example would be: "Everyone in the room is pretty and smart". It does not imply that there is a pretty, smart person in the room, because it does not state that there is a person in the room.

...In modern logic, the presupposition that a class has members is seen as unacceptable.

The wikipedia article about vacuous truth discusses arguments for treating none, some, or all vacuous truths as “true”. (An argument related to non-equivalence of the example sentences is that the Implies operator and the Logical AND operator are not equivalent.)

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I cannot think of a single scenario where you would talk about “(not) every X is …” without it being known from context that X does in fact exist. “Not every human is a man” certainly implies that humans do exist in my brain. If someone said to me, “Not every nagwoyg is a man”, my immediate and logical retort would not be, “Do nagwoygs exist?” (or, “Is there such a thing as a nagwoyg?”), but rather, “What is a nagwoyg?”, on the assumption, induced by the sentence, that nagwoygs do in fact exist. –  Janus Bahs Jacquet Jul 21 '13 at 20:46
    
@JanusBahsJacquet, even if you cannot think of such a scenario, they exist. I added some references. –  jwpat7 Jul 22 '13 at 0:11
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I am no mathematician or logician, but even if “Everyone in the room is smart” does not necessarily mean there is anyone in the room, “Not everyone in the room is smart” does (in my head). Saying that the subset of smart people in the room comprises less than 100% of all people in the room to me indicates that there must be something to take percentages out of. A negated empty set cannot semantically function as a subject in my head. Is that just me? –  Janus Bahs Jacquet Jul 22 '13 at 0:27
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To be more precise, “Not every X is Y” to me implies that some Xes are Y, which in turn requires their existence. –  Janus Bahs Jacquet Jul 22 '13 at 0:30
    
The originally quoted "Every human is not a man." is clearly a language error, and nothing more -- the intent was to say "Not every human is a man." This movement of not to the wrong place is unfortunately quite common, particularly among poorly educated Americans (i.e., the majority). –  Phil Perry Mar 14 at 16:23

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