In the short sentence "Sort by extension.", is the word "by" being used as a preposition or an adverb?

When I look it up in an English dictionary, one of the examples inclines me to think it's being used as a preposition:

  1. With the use or help of; through: We came by the back road.

Is it, in fact, being used as a preposition, or am I mistaken?

  • 3
    Yes: "by" is a preposition with the noun "extension" as its object. The PP "by extension" then functions as an adjunct expressing how something is to be sorted.
    – BillJ
    Feb 20, 2021 at 17:34
  • 1
    @BillJ Thanks Bill. If you're rather sure of the accuracy of your comment, feel free to post it as an answer so I can upvote it. Feb 20, 2021 at 17:37
  • 1
    Answer posted, as requested.
    – BillJ
    Feb 20, 2021 at 19:12

1 Answer 1


[1] Sort [by extension].

[2] We came [by the back road].

In these examples "by" is a preposition functioning as head of the bracketed PPs (preposition phrases).

In [1] the PP is an adjunct expressing how something is to be sorted.

In [2] the PP is a complement of "came". PPs expressing path are complements because they have to be licensed (specifically permitted or required) by a verb of motion like "come"

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