If I write a sentence that makes use of two verbs each relying on a different preposition, is it advisable to add commas to structure the sentence and to guide the reader, or is it not necessary (or even detrimental) to do so?

An example:

It has now become clear that Mister Smith had knowledge of, and in fact drew upon, Mister Brown's book.

What about phrases such as the following:

This seems to be the backbone to, and the original contribution of, Mister Brown's book.

2 Answers 2


Yes, it is absolutely necessary.

The information set off in the commas are a parenthetical aside, which require being set off in someway from the text. This is usually done with commas (as you have), or m-dashes (—), or just parentheses.

The rule of thumb I learned is this: If you can remove the phrase and still have a complete sentence, it is an aside.

Better link for the definition and use of asides.


I can see the above example going both ways in relation to necessity:

It has now become clear that Mister Smith had knowledge of, and in fact drew upon, Mister Brown's book.

If Mr. Smith's drawing upon Mr. Brown's book is just color commentary, then it's not necessary, i.e., non-restrictively.

If, by contrast, the context was some kind of investigation, wherein Mr. Smith's knowledge was only one of two necessary, incriminating criteria for determining plagiarism, then the fact of his having both known and drawn from Mr. Brown's book becomes necessary information, i.e., restrictive.

By the criterion of restrictive/non-restrictive, the phrase "and in fact drew upon" may or may not require a comma offset.

I point this criterion out, primarily because the other answer applies a totally different criterion, namely that of maximal simplicity.

  • Hello, Joshua. While zero punctuation around parentheticals can often make parsing somewhat harder, in simple cases it's by no means absolutely forbidden. The best rule of thumb here is to decide whether you (assumed a competent native speaker) prefer pauses to offset. Commented Jan 18, 2023 at 16:05

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