a case in which something should be done
the condition of [being logical supposed to]
必然のこと.
something that is inevitable
It is certain.
当然であること
確実なさま
なる
It ought to be so―That is as it should be―That's only right and proper―That's quite proper and as it should be―It is quite natural that it should be so―(It is) no wonder (that it should be so).
俗になる
当てにするもの
something one expects