When to use double negatives in written English?

Question

I have always been a little confused as to when to use double negatives when writing (I am unsure if this is what they are termed in English, it is the term used in Mathematics). E.g. when to use: > "I am not staying!" Thus using two negatives - `not` & `staying` ...as opposed to: > "I am going!" Here using a single positive - `going`. Both sentences begin with `"I am..."` which infers that the person is going to do something, but then this can either be followed by two *negatives*, so to speak; `"...not staying"` which cancel each other out and mean `going`, or it can simply be followed by the word `"...going."` In Mathematics a double negative is equal to a positive, and this also seems to be the case in the English language (and perhaps others). However when to use either one seems up for debate. There are plenty of other examples, e.g. `"I am not unregistered."` or `"I am registered."`

Answer 1

Thank you for your question. The example that you give, “I am not staying,” is not a double negative; it is simply an alternate way of conveying the information “I am going.” Your second example, “I am not unregistered,” is also an alternate way of expressing that you are, in fact, registered. You will find this style often in classic novels from previous centuries. An example in my own words would be: “He was not unhappy that he had to prolong his stay.” Obviously, the meaning is that he was happy. It is simply stylistic.

On the other hand, a true double negative is incorrect English: “I didn’t do nothing.” As my teachers drilled into me in school, if you are saying that you “didn’t do nothing,” then you did do something. The correct way to express this is: “I didn’t do anything.”  

I hope this helps.