以为 yǐwéi
以为（yǐwéi）means “以为: (mistakenly) think/assume — turns out not to be so”. 以为 introduces a belief the speaker held that turns out to be wrong. Formation: 主语 + 以为 + 想法（常与事实不符）
以为: (mistakenly) think/assume — turns out not to be so
HSK4Formation
主语 + 以为 + 想法（常与事实不符）
Explanation
以为 introduces a belief the speaker held that turns out to be wrong. Unlike neutral 觉得/认为, 以为 almost always carries the sense 'I thought X, but actually not X'. It looks back on a mistaken assumption, so it is usually followed or implied by a contrary fact. 我以为你不来了 means 'I thought you weren't coming (but here you are).'
Examples
Note
Almost always implies the thought was wrong. Contrast with neutral 觉得/认为.
FAQ
以为 — what does it mean and how is it used?
以为: (mistakenly) think/assume — turns out not to be so. 以为 introduces a belief the speaker held that turns out to be wrong. Unlike neutral 觉得/认为, 以为 almost always carries the sense 'I thought X, but actually not X'. It looks back on a mistaken assumption, so it is usually followed or implied by a contrary fact. 我以为你不来了 means 'I thought you weren't coming (but here you are).'
以为 — how do you form it?
主语 + 以为 + 想法（常与事实不符）
以为 — any usage notes?
Almost always implies the thought was wrong. Contrast with neutral 觉得/认为.