これが導入された場合、itは文法上の主語となるが意味を持たず、意味上の主語は動名詞/不定詞/that節などの名詞節で後続に示される。したがって、この文には2つの主語が含まれる。
- It is difficult for me to play tennis.
（to以下が本当の主語だが、文頭に置くと長すぎるため、仮のitを主語の位置に置いておき、本当の主語を文末に置いた。）
［to不定詞］
- It is always nice to barbecue outside in the sun.
- It’s important to wear a helmet whenever you do any dangerous sport.
- It thrilled her to be invited there. （感激した）
- It gave him a pain in the head to walk around ruins.
- It would be wonderful for you to stay with us.
［動名詞］
- It was no good coming there again.
- It is no use crying over spilt milk.
- It was a pleasure seeing you again.
［接続詞が導く名詞節］
- It was lucky that she agreed to undertake the job.
- It did not occur to her that the idea was his.
- It is doubtful whether the rumor is true or not.
- It is clear he tells a lie.
※接続詞thatはよく省略される
［間接疑問文：接続詞が省略されていると考えられる］
- It is a mystery why Jack killed his wife.
- It does not matter how slowly you go so long as you do not stop. （so long as：～する限り）
- It is uncertain which item he will choose.
課題 #02
