보다 means "to see," and its passive is, 보이다, which means "to be visible." The negative form of 보이다 is 보이지 않다, which means "is not visible." If you wanted to say, "The mountain is not visible," you would say, 산이 보이지 않다." Therefore, wouldn't 눈이 보이지 않다 mean "(Someone's) eyes are not visible"?
My dictionary says that 눈이 보이지 않다 means "to be blind," but if that is the case, then how do you say, "(Someone's) eyes are not visible" because of long hair, a veil, sunglasses or whatever? What's the deal?
My theory is as follows:
눈이 보이지 않다" can mean both "eyes are not visible" and "blind," depending on which 보이다 is used.
There are actually two 보이다s. One is the passive 보이다, which means "to be visible," and the other is the causative 보이다, which means "to show." The passive 보이다 is used when you want to say someone's "eyes are not visible," and the causative 보이다 is used when you want to say someone "is blind."
The causative 보이다 is a transitive verb. That means it can be used with an object. When Koreans say 눈이 보이지 않다 to mean "blind," however, they have omitted the object and are literally just saying, "Eyes do not show." However, the implied meaning is, "The eyes do not show anything," which would be "눈이 아무것도 보이지 않다." A blind person's eyes do not show anything.
Since the sentences for "eyes are not visible" and "blind" are written the same, the only way to distinguish between them would be to look at the surrounding sentences. However, since 눈이 멀다 also means "to be blind," why not use it to mean "blind," and save 눈이 보이지 않다 to mean "eyes are not visible"?
Words and expressions related to "eyesight"