What happened in "There ain't no such thing as ...."

[aheart]

Why there're two 'no's just to express the same meaning with one 'no'?
This is the question from one of my students. How can I make him understand?

[Davox]

Why there're two 'no's just to express the same meaning with one 'no'?
This is the question from one of my students. How can I make him understand?

Understand what?  That sometimes native speakers make grammar mistakes too?  Especially when speaking?  And that sometimes those mistakes become so common that they essentially become part of the language?

...actually that sounds like it really might be hard to explain if your student's English isn't great.

[shmoogrin]

This is a dialect of English with special rules that do not follow the regular grammar rules.  I am sure that someone with more experience or knowledge would be sure, but this could be Ebonics .   

[Jozigirl]

"ain't no" is Ebonics (Black American dialect) which has become popular in spoken English.  However, I would agree that it's popularity in use is mostly in America and that it isn't as widely used in other English speaking countries.

The 'rule' in English with a double negative is that they cancel each other out and actually create a positive.  ie. "There ain't no such thing as..." would, in theory, mean "There is such a thing as..."  A classic example of this is the Pink Floyd (I think?) song, "Brick in the wall" - "We don't need no education" means "We do need an education."

However, I'm pretty sure that this rule is not applied in Ebonics, so you can explain it as a dialect specific to Black Americans (probably simplest), or as a double negative that actually creates a positive.  I'm also sure, however, that there are many people who are going to disagree with me. 

[brandn14]

I'm a descriptivist grammarian.  It means  I simply tell students this is how things are said while also explaining there are two negatives or Double Negatives "aint no".  I don't care for wrong or right because
it is used in spoken English like it or not (not in writing though unless on chats).  To me, it's fine as long as it's not in an essay (writing needs to be the same for everyone to communicate effectively).   

Prescriptivist grammarians would tell you what's right or wrong in their mind and tell the world the rule of the land as they see fit.  Pick your type, but always explain why things are the way they are.

[CeilingofStars]

Standard English is fairly unique in its analogy between negatives in language and negatives in math, meaning that two negatives cancel each other out.  In most other languages (including Korean), two negatives simply strengthen the negative meaning of the phrase.

However, there are many, many exceptions in specific dialects.  It is true that AAVE - African American Vernacular English, sometimes imprecisely (and slightly offensively) referred to as Ebonics - is one of these dialects.  However, there are others too.  Many varieties of Southern American English use the double negative this way, as well as most varieties of colloquial British English.  Incidentally, an example of this is the British band Pink Floyd's song that sasez referenced.  Unfortunately, s/he actually misunderstood the lyric "We don't need no education," to imply a positive meaning (i.e. "We need an education."), when actually I think it's a pretty clear example of the amplifying effects of a double negative.

You can tell your student that it's the same as Korean.  For example, "나는 책이 별로 없어요," means "I barely have any books," but the literal translation is, "I barely don't have any books," because both 별로and 없다 are negative.  There are a hundred more examples that I'm sure others can think of more quickly than I can.

But brandn14 is right that students should be taught not to use double negatives in essays unless they're attempting to imply a mild positive.  (e.g., "Tom is not unattractive.")  Especially as English teachers, I think it's our responsibility to introduce students to both colloquial language we hear in everyday life as well as formal language used in business and writing, and to teach them the differences in usage between the two.

[Jozigirl]

However, there are many, many exceptions in specific dialects.  It is true that AAVE - African American Vernacular English, sometimes imprecisely (and slightly offensively) referred to as Ebonics - is one of these dialects.  However, there are others too.  Many varieties of Southern American English use the double negative this way, as well as most varieties of colloquial British English.  Incidentally, an example of this is the British band Pink Floyd's song that sasez referenced.  Unfortunately, s/he actually misunderstood the lyric "We don't need no education," to imply a positive meaning (i.e. "We need an education."), when actually I think it's a pretty clear example of the amplifying effects of a double negative.

I disagree with several points here.  Ebonics is an accepted linguistic term that refers to African American Slang - their vernacular language would still be English while their 'dialect' (although still somewhat imprecise) would be Ebonics.  In addition, while it is true that there are many dialects of English that utilise a double negative, it is still considered a form of slang to a certain extent in many of these dialects - ie, it's the colloquial version rather than the norm.  Your reference of British English dialects, in particular, is an example of this.  Finally, the reference to the Pink Floyd song: I don't think I've misunderstood the lyrics.  If you listen carefully to the overall message, the statement does become a positive.  The song actually reinforces the idea that education is important at a time when many students were rebelling. 

[shmoogrin]

I am glad someone with more knowledge of linguistics followed up - and of course I am glad my post, while limited, was essentially correct!