1.guess偏重“猜对,猜中”
guess a riddle猜中谜语；
2.guess at“推测”
guess at a riddle猜谜,
也可以跟宾语从句:
I can't even guess at what you mean.
我猜不着你的意思；
3.guess经常用于口语中的“以为,相信”
I guess it's going to rain.
我想天快下雨了；
My guess is that...我认为...；
4.think比较正式,语气更强,更重在表达心里的意愿,
“以为,猜想”
I think him honest.我认为他是老实的；
I thought to find you in the library.
我原来猜想会在图书馆里找到你.