句首「（as）a/an +名詞」，可以指主語以外的成分
一般來說，比較常見的句式是這樣的，as結構與主語關聯：
1.As a scientist，he was dedicated to the truth.
作為一名科學家，他獻身於真理。（《英語常見問題解答大詞典》）
2. As a parent, I feel that more should be done to protect our children. （《朗文高階》）
身為家長，我覺得應該多做些事來保護我們的孩子。
3. As a young man, Eliothad studied art in Paris. （《朗文高階》）
年輕時，艾略特在巴黎學畫畫。
4. As a pacifist, I'm againstall wars. （Merriam-Webster'advanced Learner's Dictionary）
但有時候，as指主語以外的成分，或者與主語的定語關聯：
5. As an outsider, the Koran strikes me asa reforming book, trying to return Judaism and Christianity to their origins, much as reformers attempted to do with the Christian church centuries later. (Tony Blair, Foreign Affairs, Jan. /Feb. 2007)
對於我這樣一個身處其外的人來說，《古蘭經》給我的印象是一本改革的書，它要讓猶太教和基督教回到自己的本源，正像幾個世紀以後基督教會內部的改革派所企圖做的那樣。
【分析】句中as an outsider指賓語me的身份，而非主語theKoran。
6. As a doctor, my duty is to preserve life. 作為醫生，我的義務就是維護生命。
【分析】句中as a doctor和主語的定語my關聯。
7. As a British ambassadorin that period, his advice to London heavily favored the opposition. 作為那個時期的英國大使，他向倫敦提出的主張明顯地偏向在野派一方。次
8. As theLeon County supervisor of elections, Jon Sancho's job is to make sure voting is free of fraud. (The Washington Post, Jan. 22, 2006, A6) 作為萊昂郡的選舉督察員，桑卻的任務是保證選舉不出現舞弊現象。
9. An instant bestseller across the North, the book’simpact matched that of Tom Paine’sCommon Sense in 1776.
（American History: A Very ShortIntroduction）
10. Albert Einstein was born in 1879．As a child，few people guessed that he wasgoing to be a famous scientist whose theories would change the world． (2015浙江高考英語——這個題目我請教一些老外，他們都覺得As a child後面直接是fewpeople有些辣眼睛)
總結，例句1-4是常態，是規範用法。例句5-10給說話人或者寫作者帶來方便，但有時候會引起爭議。比如例10，老外就覺得不合適。