"I don't know nothing" vs "I don't know anything" [duplicate]

Possible Duplicate:
Is there a rule about double negations that aren't meant as double negations (e.g. “We don't need no education”)?
Double negation  

I'm not a native English speaker, and this question may be very basic, but I want to learn English better, so don't hurt me with downvotes.

What is the difference between "I don't know nothing" and "I don't know anything"?

Do they have the same meaning or opposite ones?

There is no semantic difference between these two:

• I know nothing about that.
• I don’t know nothin’ about that.

The difference is one of register alone, where the first is standard English and the second is perfectly common but far more casual, and is not generally considered acceptable in formal writing save as reported speech.

Please note that the second one is not a double negative, for if it were, it would be a positive! And it’s not. Consider this contrasting pair to see the difference:

• I don’t know nothin’ about that. (reinforced negative)

• I don’t not know anything about that. (negated negative)

The two components of this second pair are no longer equivalent. The second is-at last a true double-negative. The first is merely a single negative reinforced through reduplication, which is why it still has negative sense. The true double-negative alone has positive sense.

In English, a double-negative makes a positive, just as a double-positive makes a negative.

• In the not utterly unlikely circumstance that you really do come up with such a thing as a double-positive, surely it must mean the same as a single-positive!
• “Yeah, sure.”