形容詞＋that節 − Adjectives followed by That-Clause
IT IS + 形容詞 + THAT節
I think, I am sure 等で、「彼がやったに決まっている」「彼は来れそうもない」といった表現をする事ができますが、この他にも
It is + 形容詞 + THAT節
で、「〜にきまっている」とか「〜だろう」を表す事ができます。
It was evident that she was unhappy.
It is obvious that she is lying.
It was certain that he did it.
It is unlikely that he comes to the party.
It is + 形容詞 + THAT-節を取るのは、主に下記の形容詞です。
true, apparent, evident, clear, obvious, certain,
probable, likely, possible,
unclear, uncertain, improbable, unlikely, impossible,
essential, critical, important, vital, necessary,
It is + 形容詞 + THAT-節を使った表現の便利なところは、I を主語にした場合より客観性が出る点です。
It seems certain that he bill will pass the Congress next week.
I am certain that he bill will pass the Congress next week.
It is not certain where he went.
I am not sure where he went.
このIT は、仮主語（形式主語）のIT で、THAT-節が実際の主語というのが文法的解釈です。主語になる節ですから、名詞節です。
certain, uncertain を除いて、It is + 形容詞 + THAT節 を取る形容詞は、人を主語にしません。
It's possible that she got lost on her way to come here.
× She is possible that she got lost on her way to come here.
It became apparent that we were in serious problem.
× We became apparent that we were in serious problem.
unclear, uncertain や、not certain, not clear 等は、IF-節や、WH-節をとって、「〜かどうか不明」という言い方をします。
It is not clear what the picture wants to say.
It is uncertain if we finish all by tomorrow.
下記の形容詞は、THAT-節で、動詞の原型を取る事があります。should が省略された形と取れます。テスト頻出です。
essential, critical, important, vital, necessary,
It is important that they be on time.
It is necessary that someone take a risk.
