把主語說兩次，是不是很囉嗦？如果想把兩個主語相同的句子合併，怎麼辦？非謂語動詞就是應付這類囉嗦的利器之一。

在狀語從句裡，把從句主語省略掉，謂語變為非謂語即可。可以把這種變化理解為語言向簡化方向的演變。

變化後，從句失去主語，借用主句的主語，謂語變為非謂語，成為狀語短語修飾主句，從而和狀語從句表達的意思一樣。

此外，即使兩個句子的主語不一樣，也能變為獨立主格。所以，狀語從句轉換為非謂語動詞作狀語，沒啥大驚小怪。

且看下面的例子：

不定式

If you want to marry my daughter, you have to be excellent first.To marry my daughter, you have to be excellent first.想要娶我女兒， 你首先要變得卓越。

現在分詞

When she heard she gained full marks in the test, she could not help smiling.Hearing she gained full marks in the test, she could not help smiling.在聽到自己在測試中得了滿分後，她禁不住笑起來

過去分詞

If I was given more time, I can do it much better.Given more time, I can do it much better.如果給更多時間，我能做得更好。

非謂語(成分)，顧名思義，就是不做謂語但可做主語、賓語、定語、狀語、補足語的成分。

獨立結構，說全了叫獨立主格結構，是附加邏輯主語的非謂語形式。你給的例子，Being a boy, I fell in love with her.中的句首狀語Being a boy 的邏輯主語就是句子的主語，因此不是獨立結構。

替代狀語從句的獨立結構有二：①for/with+邏輯主格+不等式/動名詞/過去分詞，②介詞+邏輯主語所有格+動作名詞。以下舉幾個例子。

例1.The lady went into a dark room, followed with a maid.夫人走進一個陰森森的房間，後面跟著一女僕。說明：伴隨狀語也可寫成：with a maid following.

例2.For/With the old here liking square dances, Bob is often upset.由於附近老人喜歡跳廣場舞，鮑勃經常不得安寧。說明：句首狀語的非謂語liking也可寫成to like.

例3.For/With the products stolen in the mart, the firm set up several monitors.由於超市貨物遭偷竊，店家在好幾處安裝了監視器。

例4.On my attention of his articles, you may attend as well.只要我關注他的文章，你不妨也跟著關注。說明：my是動作名詞attention的邏輯主語，這樣寫更簡潔。

例6.In teacher Liu"s guiding, my son has got a great advance.由於劉老師的輔導，我兒子進步很大。說明：句首狀語也可寫成：With teacher Liu guiding.

小結：獨立結構，邏輯嚴謹，簡潔明快，幾乎沒有時態限制，可最大限度減少資訊冗餘，是英語入門的一個關鍵。記住這六個範例喔！

糾正一下，是含有狀語從句的複合句變為簡單句時，要將狀語從句變成非謂語形式。即V—ing,V—ed，-to do形式。

1.分詞作時間狀語，常用在when， while，before，since，as引導的原因狀語從句中。 He listened to music while walking.(= while he walked). 他邊散步邊聽著音樂。

When completed(= when it is completed), the building will be painted white. 這幢樓在竣工後，將刷成白色。

2 .作原因狀語，相當於because，since，as 引導的原因狀語從句。 Not understanding this, he asked the teacher about.= Because he didn’t understand this,he asked the teacher about it. 因為不理解，關於那個問題他問了老師。

3 .作條件狀語，相當於if， unless引導的條件狀語從句。 Working hard, you’ll succeed. = If you work hard, you will succeed. 如果努力學習，你會成功的。

Given more time, he can finish the work. = If he is given more time, he can finish the work. 如果多給他點兒時間，他就能完成這項工作。

4 .作結果狀語。 His parents died from the accident, leaving him alone in the world. 他的父母死於車禍，獨留他於世。 【特別注意】過去分詞一般不作結果狀語。

5 .作方式或伴隨狀語。The teacher came in, followed by some students. 老師走了進來，身後跟著一些學生。

6 .作讓步狀語，相當於though， although， even if等引導的讓不狀語從句。 Lacking of money, he is happy every day= Though he lacks money, he is happy every day. 雖然缺錢，他每天還是開開心心地過日子。

7.作目的狀語。To catch the early bus,he has to get up very early.=In order that he can catch the early bus,he has to get up very early.為了趕上早班車，他必須早早起床。

而獨立主格結構是由兩部分組成，前一部分是名詞或者代詞，後一部分是非謂語動詞(不定式、現在分詞、過去分詞)或形容詞、副詞、名詞或介詞短語。前後兩部分具有邏輯主謂關係。 非謂語動詞作狀語，其邏輯主語須與主句主語保持一致。若不一致，非謂語動詞形式須另帶主語，從而構成複合結構的形式作狀語。這種結構稱為“獨立結構”。其中，非謂語動詞主動用現在分詞，被動用過去分詞。

例如:Weather permitting, we will go there. 如果天氣允許，我們就去。

His wallet stolen, he had to walk home. 錢包被盜了，他只得步行回家。

She lay there thinking, (with) her hands(crossing)behind her head. 她雙手交叉放在頭下，躺在那兒思考。

您舉的這個例子不是獨立主格結構，就是一般的非謂語動詞。要回答你的問題，首先您要知道英語句子成分可以由詞（大多為實詞）來擔任，可以由短語來擔任，也可以由句子來擔任。When I was a boy是句子作狀語，一般的狀語從句和定語從句都可以改成非謂語動詞作狀語和定語。非謂語動詞作定語或狀語與狀語從句和定語從句的意思和語法功能是一樣的，只是語法結構不同而已,一般都可相互轉換。例如：When she found the course very difficult, she decided to move to a lower level.可以把狀語從句改成非謂語動詞作狀語：Finding the course very difficult, she decided to move to a lower.又如：Lionel Messy,who has set the record for the most goals in a calendar year, is considered the most talented football player in Europe.可以把定語從句改成非謂語動詞作定語：Lionel Messy,having set the record for the most goals in a calendar year, is considered the most talented football player in Europe.