Cannot is formal, while can't in informal.
"Cannot" and "can not" are interchangeable, but when you are asking question for example:
"why can't I...", you can also say "why can I not..." (which is more formal), but you can't say "why cannot I..."
subordinate clause
A subordinate clause is a group of words with a subject and a verb, that cannot stand alone.
Nick means that people can fit into only one of these four categories, which show that no one is truly happy in their lives.
Gatsby and Tom are the pursuing, Daisy is the pursued, Jordan is the busy (too busy to care about anyone else or being a good person), and Nick is tired. He's tired of having to deal with everyone else's drama and problems.
