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Grammar is of no help in differentiating between partial and full negation. Native English speakers use meaning and context to make the differentiation when telling them apart in written or spoken English. However, negation is not just simply a matter of partial negation vs. full negation. We also have two more types of negation: “idea negation“ and “combined effort negation“ (which will be explained below).
Here are some general patterns that might be of some help to non-native speakers in constructing sentences expressing partial and full negation:
The “all … not” construction and the “not all” construction are generally used for partial negation. Thus, in your example from Shakespeare
All that glitters is not gold
we have partial negation, and we could express the idea equally well with the construction:
Not all that glitters is gold.
Notice that both forms have the same meaning: “Some things that glitter are gold and some are not.” This is partial negation.
Some more common examples of partial negation are:
All men are not jerks. [= Only some men are.]
Not all men are jerks. [= Only some men are.]
All that you see in this room is not mine. [= Only some of it is mine.]
Not all that you see in this room is mine. [= Only some of it is mine.]
Sometimes, there is a slight difference in meaning between the two forms. For example:
All humans are not born equal.
is a negation of the statement “All humans are born equal.” The speaker wishes to contradict (or “negate”) a commonly accepted idea. However, if someone says:
Not all humans are born equal.
he or she would mean: “Most humans are born equal, but there are a few exceptions.” The difference between this example and the previous two examples is that “All humans are born equal” is a well-known and widely accepted idea, so negating the idea is different from the usual partial negation vs. full negation distinction. This is “idea negation“—something quite different from partial and full negation.
If we want to express full negation, we use “none“ or “nothing“ or “no one“ or “no + NOUN.” Thus, if we wanted a full negation in Shakespeare’s sentence, we would say:
Nothing that glitters is gold.
Of course, the sentence would not be true, since gold actually does glitter. But we would, grammatically, have a full negation, even if the meaning is “wrong.”
In your next example sentence, we would not construct a sentence such as “All the answers are not right.“ if we wanted a full negation. We would say:
None of the answers is right.
Not (even) one of the answers is right.
Not a single answer is right.
No answer is right.
If we really wanted to use “all” in this case, we would not construct a negative sentence, that is a sentence containing a negated verb. We would construct an affirmative sentence, such as:
All the answers are incorrect.
All the answers are wrong.
This is an indirect form of full negation. It is indirect because we are not using negation, but a word with a negative meaning (“incorrect” or “wrong”).
We can use the “all … not“ construction to express “combined effort negation.” The most well-known example of this type is the line from the nursery rhyme “Humpty Dumpty”:
All the king’s horses and all the king’s men could not put Humpty together again.
Note that this means: “The combined effort of the king’s horses and the king’s men was not able to do the job.” This is not full negation. If we wanted full negation, we would have to say:
None of the king’s horses and none of the king’s men could put Humpty together again.
Combined effort negation is what we have in your example sentence:
When the time comes, not all the angels in heaven shall save him.
This sentence from Emily Brontë’s Wuthering Heights means: “The combined effort of all the angels in heaven will not be able to save him.” It is not an example either of full negation or partial negation. As you can see, this is an example of combined effort negation, which is something different altogether.
One more example of combined effort negation comes from Shakespeare’s Macbeth, in which Lady Macbeth says:
All the perfumes of Arabia will not sweeten this little hand.
What she means is: “Even if I use all the perfumes of Arabia together in combination with one another, I will not be able to remove the smell of blood from my hands.”
Finally, we need to look at your very first example sentence: “All civilized people can’t be cannibals.“ This is not a sentence that a native English speaker would construct. There is no occurrence of this sentence on any English website or in any English book on the entire Internet. The sentence has no meaning in English. It is simply not the way native English speakers think. The very content of the sentence is meaningless. In English, being civilized automatically rules out the possibility of being a cannibal. That is why the sentence is meaningless. The sentence has the form of idea negation described above (“All humans are not born equal”) and it therefore implies that the generally accepted idea is that all civilized people are cannibals. Of course, there is no such generally accepted idea. That is why the sentence is meaningless. In English, we would say:
No (normal) civilized person can be a cannibal.
There is no other way to say this. Of course, there are a few civilized people (very few, actually) with severe mental problems who eat human flesh, or do so out of sheer necessity to survive, but this is not what your example sentence is speaking about. There have been a few cases of civilized humans eating the flesh of other humans in order to survive, but they would not be called “cannibals,” since they do not practice cannibalism. There have also been a few cases of civilized people with mental disorders who have eaten human flesh. They can be called “cannibals” because their eating of human flesh was not purely for survival purposes, but they would be regarded as extreme exceptions (or “aberrations”). If we were talking about such people or we had such people in mind, we would say:
Not all civilized people avoid cannibalism.
Not all civilized people refrain from cannibalism.
This is how we would achieve partial negation in this case.