nominals係列

不定詞之所以叫不定詞,就係因為To+infinitive的詞性不定,除了形容詞及副詞,它比介詞短語更多功能,可作名詞:

I hope to win the lottery. 

句中的to win the lottery是hope的受詞, 又或:

To succeed is my goal. 

句中的To succeed主詞也是名詞.

留意不定詞主語可以延後,英文叫extraposed subject:

It is dangerous to swim in bad weather.

句子的it究竟指什麼呢? 中學時我也有概念, 便是這個it 其實是代替句子的尾部,即to swim in bad weather這infinitival clause (不定詞子句). 換句話說, 句子本身是這樣的:

To swim in bad weather is dangerous.

由於句子主語太長,我們便將它放到最後,而以it 去代替其位置. 這個it, 英文叫anticipatory it或introductory it.句子文法上的主語 (grammatical subject)是it, 但詞義上的主語(semantic subject)卻是to swim in bad weather.

以上例句的主語to swim in bad weather 不是很長, 延後不延後似乎沒有特別差別;但有時候主語可以很長,例如:

It is gratifying to note that more people are realizing the harm of eating fast food.

句子「詞義主語」是 to note that more people are realizing the harm of eating fast food. 如果用它作「文法主語」,便會「頭大身細」:To note that more people are realizing the harm of eating fast food is gratifying.  在這種情況下, 把主語延後,便可使句子更易理解.