Is a person impressed by or with?

Answer 1

This is just a theory and would love to be corrected if necessary, but..

..my guess is that "with" means "to combine two or more different things", like a conjunction.

For example: "a drink with jam and bread"

In the Greek language, such a conjunction could be expressed with the word "meta", which has become common in plenty of languages.

"By" is rather meant to express causality: one thing leads to another.

In this case, some sort of event / thing leads to a person (or a group of persons) being impressed, so I'd have to opt for "by".

In the Greek language, such causality is probably expressed by using the dative grammatical form.