幾時會用到inversion(倒裝句)?

你好～
是否使用倒裝句要視乎句式的情況，而不是只考慮informal或formal的場合。

請看：
http://englishwizard.mysinablog.com/index.php?op=ViewArticle&articleId=1880591

倒裝句（Inversion）動詞一般放在名詞後面。動詞放在名詞前面的，叫倒裝句。（A verb normally follows a subject. Inversion occurs when a verb is put before a subject.） 使用倒裝句的情況： l 問句（Questions）l 在具有「限制」或「否定」意義的副詞之後（after restrictive or negative adverbs）l 用副詞表示地點時（adverbial expression of place）l 在neither、nor和so之後（after neither, nor and so）l 在so, that, often 和 to such lengthsl 條件句 問句用倒裝StatementsQuestionsHe was there.Was he there?She did allow him in.Did she allow him in?You have seen it.Have you seen it? 在具有「限制」或「否定」意義的副詞之後（after restrictive or negative adverbs）用倒裝l 為了強調（for emphatic purpose），具有「限制」或「否定」意義的動詞（adverbs with restrictive or negative meaning）可以放在句子的開頭。取決於動詞的結構，有兩種情況：（a）動詞有助動詞的話（例：在had left和must enter裡，had和must是助動詞），助動詞要放到主詞前面，主要動詞放在主詞後面；（b）動詞沒有助動詞的話，就須要加上do、does 或did等，都放在主詞前面，主要動詞放在主詞後面。l 具有「限制」或「否定」意義的動詞包括：little, never, seldom, rarely, hardly, scarcely　（註：句式是hardly/scarcely had…before/when）, no sooner　（句式：　No sooner…than，留意no sooner 要配than而不是before或when）, under no circumstances, on no account, in no way, at no time, nowhere, not till, not only…but also, only then, only by, only when.l Little did he know what he was thinking.l Scarcely had I left home when/before it started to rain. （＝I had scarcely left home when/before it started to rain.）（我剛出門就下雨。）（另一種很簡單的寫法是：It started to rain just after I left home.）l Hardly had the meeting begun when/before the chairman was assailed with a tempest of jeers and angry shouts. （= The meeting had hardly begun when/before the chairman was assailed with a tempest of jeers and angry shouts.）（會議一開始，一輪暴烈的嘲笑聲、怒吼聲就襲向主席。）（另一種很簡單的寫法是：The chairman was assailed with a tempest of jeers and angry shouts just after the meeting began）l Under no circumstances must you enter that room. （=You must under no circumstances enter that room.）（你無論如何都不可進入那房間。） 還有其他，因為太長，所以請看以上連結。

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http://www.360doc.com/content/09/0530/21/0_3715093.shtml

We use inversion when we want to put the words we want to stress at the front of the sentence.

早前我上載了一些錄像在Youtube，解釋一些基本的文法規則，這個錄像正正回答你的問題
http://www.youtube.com/watch?v=P4mJS5t-xyU