想, 觉得，以为 all mean to think. But is there any subtle difference between the three or tense difference? When would you be more likely to use them in context?
[我想 + statement] the statement is what I think is true
[我觉得 + statement] the statement is what I feel is true
[我以为 + statement] the statement is what I thought was true
[我認为 + statement] the statement is what I concluded to be true
[我相信 + statement] the statement is what I believe to be true
我想他不会来了 = I think he won't come
我觉得他不会来了 = I think (feel) he won't come
我以为他不会来了 = I thought he wouldn't come
我認为他不会来了 = I think (concluded) he wouldn't come
我相信他不会来了 = I think (believe) he wouldn't come
以为 is mostly used for:
- wrongly thought/believed
我以为你死了！ I thought you were dead!
觉得 is closer to:
- feel/think (of an opinion)
你这样说，我觉得非常不靠谱 What you said is totally unreasonable.
想 is close to the English:
我想这个案子肯定有猫腻。 There's something fishy about this case.
In Chinese the idea of English 'think' is hardly ever used - even in English it's mostly just a buffer or fluff; if anything 觉得 is the closest.