Comma and inversion

Question

I just wrote an English exam and I'm not sure if these two sentences which I've written are correct. If they're not, please tell me and if they are please back that up with a credible source.

1. Not until three years after the murder, was the murderer found.

Here I'm not sure about the comma. Is it (1) correct, (2) false or (3) optional?

2. You'd be amazed at how many arguments could be avoided by taking a simple step.

Is "taking" here used correctly? My teacher wanted to see "such" instead of "taking" but I think this is also correct.

Answer 1

In your first example, you have an adverbial phrase in an inverted sentence (which has been inverted because the adverbial is negative); there should not be a comma:

Not until three years after the murder was the murderer found.

Here’s what The Chicago Manual of Style has to say:

6.31: Commas with adverbial phrases
. . .
A comma should not be used to set off an adverbial phrase that introduces an inverted sentence.

_{Before the footlights stood one of the most notorious rakes of the twenty-first century.}

_{Source: The Chicago Manual of Style (login required)}

If you prefer a more linguistic take on it, you can root around in “Negative Inversion in Standard English”:

Another property that [negative inversion] (9) and wh-questions (10) have in common is that they, unlike Topicalization (11), do not tolerate an intonational phrase break (or comma intonation, indicated by the symbol “,”) between the fronted constituent and the rest of the sentence . . .
_{See p. 127 in the PDF accessible from the link above.}

Answer 2

You should really have asked two separate questions, but...

...by taking a simple step informs us that there is a simple step that we could take.

...by such a simple step implies that the step has already been named, but emphasises how simple it is.