N4
なくて
Not A but B; not … and …; because not …
お金がなくて車が買えない。
I don't have any money, so I can't buy a car.
Explanation
「なくて」 has 3 uses
1Not A but B
Rules one thing out and gives the right one: 「ペンではなくて、鉛筆です」 it's not a pen, it's a pencil.
あれは犬ではなくて、猫です。
That's not a dog — it's a cat.
これはペンではなくて、鉛筆です。
This isn't a pen; it's a pencil.
2Not …, and also …
Lines up a negative quality with another one: 「広くなくて、暗い」 it isn't spacious, and it's dark.
あのケーキは甘くはなくてまずいです。
That cake is not sweet, and tastes bad.
私の車は静かではなくてガソリンの減りも早い。
My car is not quiet, and runs out of gas quickly.
3Because not …
Gives a negative cause for a feeling or result: 「お金がなくて、車が買えない」 I have no money, so I can't buy a car. 「分からなくて困った」 I didn't understand and was stuck.
お金がなくて車が買えない。
I don't have any money, so I can't buy a car.
宿題が分からなくて、困りました。
I didn't understand the homework and didn't know what to do.