Live bacteria are not present in all yogurt brands.
Does it mean "live bacteria are present in some yogurt brands, but not all" or "there is no bacterium in any yogurt brand"? Or does it depend on the context?
I know that "All yogurt brands do not contain live bacteria." seems to mean "not all yogurt brands contain live bacteria". But what if "all" does not appear at the beginning of a sentence but appear after some preposition such as "in"?
I often confuse this. How should we distinguish between "partial negation" and "complete negation" effectively? I have searched for this, but the answers are quite different.