Confusing usage words part eight

In mathematics, a negative number times a negative number yields a positive number.

Similarly, in grammar, when two negative words are used (where only one is needed), the
negatives cancel each other out, making the idea positive and not negative as intended. In
the sentence, ‘‘I cannot get no respect from them,’’ the two negative words, cannot and no,
cancel each other out. Thus, the sentence is really saying, ‘‘I can get respect from them,’’
a far different thought from what seems to be the sentence’s original intention. Had the
sentence read, ‘‘I cannot get respect from them,’’ or ‘‘I can get no respect from them,’’
the meaning is quite different from that when both negative words are included in the
sentence.
Here is another example of this double negative situation. Notice the different meanings
when the negative words are included or deleted.
Two negative words in the sentence: We didn’t have no disappointments.
One negative word in the sentence:We didn’t have disappointments.
One negative word in the sentence:We had no disappointments.