Passive voice SC Page 116

[Anonymous]

I just need a clarification around the passive voice.

Should passive voice must have person performing the action.

E.g. SC Page 116

During operation, new blood vessels are inserted, bypassing blockages.

Must this sentence have "by doctor" or "by physician". For some reason, when I was studying the modifiers, I thought that it should.

[Anonymous]

Any takers for this?

[esledge]

You may be recalling OG Verbal Review (1st ed.) #38, where the person doing the action in passive voice is required. But that question had a modifier that would be left dangling without the person; he/she wasn't really required for the sake of the verb.

It's ok to leave the actor unnamed in a sentence in passive voice: The vase was broken.
By whom? Maybe we just don't know...

But this would be incorrect: Using a hammer, the vase was broken.
We may still not know who broke the vase, but we need an answer to "who was using the hammer?", i.e. the "using" modifier needs a logical noun to modify. Without a person in the sentence, it seems to say the vase was using a hammer. Either of the following would be correct:
Using a hammer, someone broke a vase.
The vase was broken by someone using a hammer.