"All that is gold does not glitter" is the first line of a poem from the Lord of the Rings and it's supposed to mean "not all gold glitters" but I'm struggling to see how this can be deduced.
If all that is gold does not glitter then it follows that "gold never glitters". If all gold doesn't glitter then there's no such thing as gold that glitters. This is quite different from the actual meaning. "Some that is gold does not glitter" would make more sense. Am I missing something? Does "all" actually mean "not all" in this context? It's really confusing.
It looks like "Not all that is gold does glitter" would mean the same thing, but in logic it has a different meaning.