Douglas Wilson, in the process of making a more extended argument, points out some of the messiness of our English language — particularly regarding the way we negate statements (or not!):
The logic of words is not the same as the detached, structural, and contentless logic of math or symbolic logic. Some quirks should help make the problem obvious. Why do ‘He could not get to sleep, not even with a sedative’ and “He could not get to sleep, even with a sedative’ mean the same thing? Why does ‘Don’t be surprised if he doesn’t get well one of these days’ mean that we should not be surprised if he does get well? Why do “I couldn’t care less’ and ‘I could care less’ mean the same thing? Who is in charge of this language?” (The Paideia of God, p. 95).