It is imperative 「that you (should) attend [for you to attend] the meeting.
その会議には必ず出席するように
It is important for him to do it.
彼がそれをやるのは重要だ（◆意味上の主語はforで示す）
It is important that exceptions (should) not be made.
例外を設けないことが大事だ
It is important to distinguish good from evil.
善悪のけじめをつけることが肝要だ
It is important 「for us to know [that we (should) know] the full truth.
我々にとって肝心なのは事実の全容を知ることだ
It is impossible of realization.
それは実現不可能だ
It is in your (best) interest(s) to study hard.
猛勉強が（一番）君のためだ
It is inconceivable that ...
…であるとはとても信じられない
It is incredible that he can't do that.
彼がそれをできないとは信じられない
It is incumbent on you to advise him.
彼に忠告するのは君の義務だ
