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Which is correct?

You may be impressed how often the technique is being used in industry.

You may be impressed by how often the technique is being used in industry.

The first one is what I get used to saying in daily life. It may turn out I've been wrong for ages. I immediately noticed there might be something grammatically wrong when I wrote it. I couldn't help but add the preposition by to make the sentence correct. Is it just a matter of style?

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In the first instance, the word by is not exactly omitted: it's said to have been elided which means that meaning-wise, it is understood by the reader, so that the sentence remains grammatically correct and complete. Voting to close as a non-Q. – Kris Dec 2 '12 at 8:20
@WillHunting You didn't say what you think it is, which would have been purposeful. – Kris Dec 2 '12 at 13:10
up vote 7 down vote accepted

No, by shouldn't be omitted after impressed.

In writing, people generally use by, with, or that after impressed

I'm impressed by his skill
"President Obama Is Not Impressed With Your Right To Modify His Photos"
I'm impressed that it's selling so well this soon.

A sentence like "I'm impressed how tall he is" doesn't sound like idiomatic native-speaker English to my ear, but I'm sure that people say and write it. A good copy editor will change it to "impressed by how tall" or, perhaps, "impressed with how tall", or "impressed that he's so tall".

Google Ngrams shows that

1 impressed by


2 impressed with

are most frequently found in books,

3 impressed that

is rarely found in books, and

4 impressed how

is never found in books. This doesn't mean that people don't say it, however: people will say anything, regardless of whether it's right or wrong.

Perhaps choosing between by and with is merely a matter of style. You'll have to decide based on context and the specific sentence whether one is better than the other. Give us some choices and we'll see what everyone else thinks -- maybe.

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You don't say whether "Impressed that" is grammatical. If it's not, it certainly is harder to fix than "impressed how"; you to say "impressed by the fact that". I'd rather be ungrammatical. (And a rather intriguing Google Ngram showing how "impressed by the fact that" is being replaced by "impressed that") – Peter Shor Dec 2 '12 at 13:48
@Peter: I think impressed that is grammatical & reasonable, but it's not always a synonym for impressed with or impressed by. English speakers are overly fond of pointless verbosities (e.g., prior to), so I'm surprised that "impressed by the fact that" is being replaced by "impressed that". I'd rather be brief in formal writing (I'm prolix when I blog & when I lecture on writing biomedical articles in English). Fowler said it was better to break the rules than to be awkward in writing (I can't remember where, though). Recasting sentences is also good. – user21497 Dec 2 '12 at 14:29

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