Way

It may be clearer if the sentences are "de-relativised":

·The greatness of human beings is celebrated by/in (such kind of) communication.
·They will become richer by/in this kind of way.

You may be able to see now that the second one should be "in".

In the first case either will work, with only a faint change in meaning. I find "Contact be

OH, so the "which" in the first example refers to "communication" not to "a way of communication", right?

Even if the article was "the (way...)" not "a (way...)", would you still think the relative pronoun refers to "communication" only?

TakaOH, so the "which" in the first example refers to "communication" not to "a way of communication", right?

No, it refers to "way of communication". The "way of" aspect got bundled into "such kind of", but I see now that the presentation may have been unclear.

I'm confused, GPY.

If it refers to "way of communication", "of communication" is a modifier of "way" and the relative pronoun is also a modifier of "way".

Then why do the first two examples work whereas only the last one of the second pair doesn't? All of the relative pronouns refer to "way", don't they?

As used in the second example, "way in which" is a kind of set idiomatic combination, referring to the way that something is achieved, or the way it happens. Adding "of communication" breaks that set pattern. Changing "way" to, for example, "method" in the second example would also break it, and it would be usual to say "That is the method by which they will become richer".

Great explanation! Thanks, GPY, as always!