1.只好：have no choice but to do sth（kind of sad and not willing to do that) for example:You and your friends were going to take a picnic.But unfortunately, it started to rain heavily when you guys were on the way.So you had no choice but to return home.(You were not willing to go home but you had to do so and you felt it was a pity.) 2.非/非得：“非” is often used with "不可" at the end,like:"非……不可" If you say "我非去不可！" to others，that means you will go regardless of any obstacles and no one can stop you.(very strong will) If others say "你非去不可！" to you, that means you must go there even if you don't want to.(like an order！） 3.必须:similar to the meaning of "非……不可",but it's sort of milder than "非……不可"（Because "非……不可" is double negative and usually double negative is a method of emphasizing what you want to say.) EXAMPLE: 那里很危险，你不能去！There is very dangerous.You cannot go there! 我必须去，我的朋友还在那儿！I must/have to go 'cause my friends are still there. 不行，你会有生命危险！No.You will be in great danger! 我非去不可！I must go!(the tone is becoming stronger and you want to emphasize waht you've said.) ----------------------------------------------------- It's all my own understanding. Hope that I can help you~ Your question is great 'cause I've never thought about the difference between those words. Really hard to distinguish!^^

1、forced to 2、have got to 3、must

我只好去（我不想去，但是没有选择，没办法，只能去） 我非去（表达了我的决心，无论怎样我都要去，什么都不能阻挡我） 我必须去（和我内心想法无关，无论我想去还是不想去，我都应该去，这是我应该完成的事） 希望对你有帮助。

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