なくちゃいけません　vs　なきゃいけません So I was looking through a Japanese as a second language textbook I had and saw the phrase "なきゃいけません" It looks kind of like the phrase I recently learned for "should do something" and was wondering if somebody could clarify If the former is just another version of the later or of there is a certain difference in nuance. I was also wondering if there were other variations. If you can as an added not-so-important question, I was wondering if somebody could also break down what these mean in more of a literal sense so I can get a deeper understanding. I know it has something to do with a double negative but where does なくちゃ come from (and can it be used on its own in some situations?) and where does いけません come from. Any help in my learning is much appreciated :D ありがとう！