"You can't afford not to buy this." That's what I said—over and over again—to a friend who was floundering on whether he should buy an Xbox controller. He ended up taking the controller home ($90 later), but he's been using it ever since.
I said it that way to be funny, but to emphasize he should buy the controller. I used two negative words and they combined to form a positive. Remember math? Multiplying two negatives makes a positive. It's like that with English too.
I hid one with a contraction (can't) but there are still two instances of the word not in that sentence:
"You cannot afford not to buy this."
"You can afford to buy this."
My friend knew what I was talking about, but negatives can get even trickier when you add more. Take this quote from family guy, for example:
"If you'll just sign this contract without reading it, I'll take your blank check and you won't not be not loving your time-share in no time."
That one is worse, especially since the salesman talks so fast. This is yet another testament to why fast-talking salesman who know their way around words are so dangerous.
The good news is that it's not impossible. Let's break this down a little, shall we?
"You will not"
So now we've got:
"...you will not not be not loving your time-share in no time."
Right, so if we think back to the math reference earlier, those two negatives cancel each other out:
not not be not loving your time-share in no time."
"...you will be not loving your time-share..."
"...you will not love your time-share."
Whew. That was a lot of work. But that's the problem with negatives: the more you add, the more work it is to decipher. That's why the writers on Family Guy wrote it for the salesman—it's sleazy, under pressure, and if you're not thinking hard enough, you'll miss it.
So remember: if you're ever faced with more than one negative, break it down and really think about it. You can often see how badly someone is trying to screw with you by counting their negatives.
And that, my friends, is not a joke.