以为
yǐwéi
to think; to believe (often with the implication that the belief is mistaken – unless referring to one's own current belief)
In a story
苏然以为他在开玩笑，可是他的脸一点儿也不像开玩笑。Su Ran thought he was joking, but he didn't look as if he was joking at all.假男朋友 · The Fake Boyfriend · HSK 5
老顾以为是自己的书好，林老师以为是自己的店干净。Old Gu assumed it was because his books were good; Ms Lin assumed it was because her shop was clean.对门 · Across the Street · HSK 6
Grammar with 以为
⋯⋯，⋯⋯倒/反倒⋯⋯
⋯⋯，⋯⋯倒/反倒⋯⋯ — yet in fact, on the contrary
不知X的
不知⋯⋯的（还以为⋯⋯）— anyone who didn't know would think
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