What is the difference between a and any in the following sentenc?
- Can a bulletproof vest stop a bulltet fired from an AK-47?
- Can any bulletproof vest stop a bulltet fired from an AK-47?
Does the second one using any mean to say "Does there exist a single bulletproof vest that can stop a bullet fired from an Ak-47"?
Hi, Subhajit: Your examples here aren't very pleasant, but you are correct that the one with "any" has the meaning "Does there exist a single bulletproof vest that . . . [etc.]?" In a normal context, that is not the desired meaning. We would simply say, "Can a bulletproof vest stop a bullet fired from this type of gun?"
If the sentence with "any" were used, it would receive emphatic stress, and there would be preceding context justifying its use with stress -- for example: "This (supposedly) bulletproof vest can't do it. Neither can that one. Indeed, I have never come across a bulletproof vest that can. Can ANY vest do it?"