以为

以为 (yǐwéi) means 'to think, to assume' — but almost always with the implication that the thought turned out to be WRONG. It is the go-to word for moments of misunderstanding: '我以为今天是星期五' ('I thought today was Friday' — but actually it isn't). Two things English speakers often miss. First, 以为 is NOT the neutral 'I think / I believe' — that is 觉得 (juéde) or 认为 (rènwéi).

Using 以为 when you simply state an opinion sounds odd, because the listener will assume your view was incorrect. Second, 以为 almost always pairs with a clause expressing what you wrongly believed, and is typically followed by a corrective ('我以为他是日本人, 其实他是中国人' — 'I thought he was Japanese, actually he's Chinese'). It is one of the most useful HSK 3 verbs because it captures a feeling English needs a whole phrase ('I was under the impression that…') to express.