▲其实，无论是表示“作为年轻人”还是表示“当某人年轻的时候”，as a young man 都是一个介词短语（即其中的 as 是介词）。比较：

As a young man, you should be active in local politics. 作为年轻人，你应该积极参与当地的政治活动。

As a young man, he was very active in local politics. 他年轻时曾积极参与当地的政治活动。

▲顺便说一句，当 as a young man 理解为“当某人年轻的时候”时，但不能直接看作是在 as 后面省略了与主句相同的主语和动词 be，因为 as 引导时间状语从句时，其谓语动词通常不能是表状态的动词 be。如：

2 He entered a monastery as a young man. 他年轻的时候就进了修道院。（= He entered a monastery when he was a young man.）

2. As a young man, he wanted to see the world before he settled down. 年轻时候的他想先去见见世面，然后再安定下来。(=When he was a young man, he wanted to see the world before he settled down.)

3. As a young man he suffered agonies of religious doubt. 年轻时，他因为对宗教的怀疑而饱受折磨。（= When he was a young man he suffered agonies of religious doubt.）

4. As a young man he was admired, but as an old man he became a figure of fun. 年轻时，他受人崇拜；到老了，却被人嘲笑。(=When he was a young man he was admired, but when he was an old man he became a figure of fun.)

5. Through the smoky prism of time, I could just barely make out my father as a young man. 时间模糊了记忆，我几乎想不起父亲年轻时的样子。(=Through the smoky prism of time, I could just barely make out my father when he was a young man.)

6. As a young man, he had been certified and sent to a hospital for the mentally ill. 他年轻时被证明患有精神病，并被送到了精神病院。(=When he was a young man, he had been certified and sent to a hospital for the mentally ill.)

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