We have known to each other or We have been known to each other?

Question

Which is the correct way to say

1. We have known to each other for many years.

2. We have been known to each other for many years.

Present perfect or present perfect continuous.

Answer 1

If you are acquainted with the other person to whom you are referring, you should say "we have known each other for many years" (like your #1, but without "to").

If you are not acquainted with the other person and mean to say only that you have known about each other for many years – that is, that each of you has been aware of the other's existence, reputation, etc. – then you can say "we have been known to each other for many years." However, for this situation many native speakers would find it more natural to say "we have known of each other for many years." (In fact, when I first posted this answer, I inadvertently substituted that phrase myself.)

Perhaps these examples will help to illustrate the difference:

Bob and I have known each other for many years; in fact, we first met when we were both in kindergarten.

Although we live on different continents, Bob Smith and I have been known to each other for many years; I've followed his research with great interest since the early 1990s, and mutual acquaintances tell me he has been familiar with my work for almost as long. I hope someday we'll have a chance to meet and possibly even work together.

Answer 2

Neither is really very natural. Number 1 above I think is actually incorrect. Number 2 is correct, but rather formal. I would be inclined to say:

We have known each other for many years.

That is a very common form.

Even if number 1 is not technically ungrammatical (as i think it is), it is not a common or natu5ral form. "We have known to" just feels wrong, and I can't make it parse.