by引導的倒裝句，only

only by引導部分倒轉句.

例如：only by working day and night can the couple pay off the debt.只有靠日夜勞作這夫婦從能還清債務。 

這個句子中，情態動詞can被移到主語the couple 前，構成部分倒轉句。

英語的“only+狀語（介詞短語/副詞/狀語從句”位於句首，句子要求用部分倒轉，其結構是：only +狀語+助動詞/情態動詞/be動詞+主語+謂語+句子的其他成分

例如：

1、Only by working hard can you succeed.

只有努力工作你才能成功。

2、Only in the reading-room can you find him.

你只有在閱覽室才能找到他。

英語中only加介詞短語放於句首，句子要進行部分倒裝。

例如

Only in this way will our school become more and more beautiful.

Only by studying hard will you have the chance to be admitted to your ideal university.

Only by listening to the teacher attentively in class will you make progress.