I read the following sentence in a paper. I wonder if I can remove the second by and why.

The refinement is done by moving the boundaries of the superpixels, or equivalently, by exchanging pixels between neighboring superpixels.

2 Answers 2


Can the first preposition by govern two objects, moving and exchanging? Of course. Some call this a species of zeugma. The problem is a stylistic one of sending your readers down a garden path, i.e., providing the opportunity to make an incorrect parse, if only temporarily. You have a comma after equivalently, a common use after any introductory adverb. But a comma also separates independent clauses, and the gerund clause exchanging pixels could make a fine subject, possibly leading your readers to expect a sentence like

The refinement is done by moving the boundaries of the superpixels, or equivalently, exchanging pixels between neighboring superpixels will do the trick.

Of course, any such readers will realize their error when they reach the end of the sentence after the final prepositional phrase. They will then go back and reparse the sentence to recognize the prepositional phrase with a compound object.

But this is bad manners as well as bad style. Leave in the second by as a courtesy to your readers.

  • So, both are right. The original one (i.e., with the second by) is better for reader?
    – aban
    Oct 8, 2016 at 8:43
  • Yes, both are grammatical and mean the same thing. It's just that without repeating by, the sentence is harder to parse. Was it clear in the explanation why that would be?
    – deadrat
    Oct 8, 2016 at 8:59
  • :) your explanation is very professional. I was just asking for sure. Thanks very much. :)
    – aban
    Oct 8, 2016 at 9:11
  • 2
    @aban. No, both aren't 'right'. There is a widespread misconception that if something is grammatical, it's automatically acceptable. Sometimes, perfectly grammatical sentences are needlessly ambiguous (which is very serious) or needlessly difficult to parse (as here). I'd knock a mark off here (in an English essay) for wilfully and nonsensically omitting a small word that makes quite a difference to ease of reading (for the reason deadrat gives). Oct 8, 2016 at 9:11
  • @EdwinAshworth Writing clear English is difficult. (Check out the small edit I made to the answer to eliminate my own bit of ambiguity.) The OP is not willful because he's having trouble coping with the unfamiliar; the OP is not nonsensical because he hasn't had enough practice to separate sense from nonsense.
    – deadrat
    Oct 8, 2016 at 9:53

Yes you can remove the second by as equivalently is by itself enough to convey the sense of by.

  • Is it better to keep 'equivalently' and the comma?
    – aban
    Oct 8, 2016 at 13:23
  • The answer? Says who? Matters of style generally don't have definitive answers. How does two words (along with) as opposed to one (by) "lighten" text? Through doesn't indicate "opposition", and any wording to emphasize "contrast" changes the meaning of the sentence, if only slightly. Most style guides would not advise a comma after superpixels and before or to avoid the very garden path I mentioned.
    – deadrat
    Oct 8, 2016 at 23:53
  • Disregarding opportunities to always better ourselves undermines ultimately the capacity to grow. 'Style' is a very important component in writing, and I wouldn't underestimate the benefits of its misconstrued futility. Using metaphoric verbs to enchant the monotony of a text is perhaps unnecessary, be as it may, repetitions are not a matter of style. Finding a synonym, is where the passion for writing begins.
    – Specialist
    Oct 9, 2016 at 22:33

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