Language

1)彼がテストに合格したことは知ってます

2)彼がテストに合格したのは知ってます

3)彼がテストに合格したとは知ってます

4)彼がテストに合格したって知ってます

I've come across these variations tons of times. Knowing that they do carry the same meaning essentially, I was asking myself if they all have the same level of politeness (except for no.4 of course which is colloquial)

In terms of meaning... 1) and 2) are idential. 4) is the same as 彼がテストに合格したと知ってます, which is identical to 1) and 2).

When you compare those sentences, 3) has a hint of something *else* - because of は in there - meaning "I know that he PASSED the test" to be followed (potentially) by something like "I knew THAT, but I didn't know that he decided not to join that school but went to work instead."

And yes, except for 4) which is just slightly colloquial (but still in polite speech), they are all of the same level of politeness.

Thanks a lot AK.

I always appreciate your help, and the help of other people here on the forum who regularely help people out with their language questions.

いつもすぐに返事してください、まことにありがとうございます。