I have a Spanish friend, who wrote the following sentence:

"How does foo, bar, baz can be compared?"

I corrected it to read:

"How can foo, bar, baz be compared?"

Other than the obvious, he has asked me to explain why the first is wrong, and the second (maybe) is correct.

Any help?


2 Answers 2


The phrase "how does ...?" is singular, so the reader will always expect a single entity to follow. For example: "How does magnetism work?" or "How does a bird fly?"

The plural version would be "how do ...?" as in: "How do flowers grow?" or "How do John and Mary know each-other?"

In either case, using the verb "do" implies that there is a single, correct answer to the question. In your sentence (unless I have misinterpreted it), the intent is to ask a more open-ended question. This meaning is expressed by using "can" instead of "do".

To illustrate, if you were to ask: "How do foo, bar and baz compare?" A single answer is expected. As in: "Foo is better than bar, but baz is the best because ...". Asking the question using "can" instead of "do" allows the reader more freedom in answering. For example: "How can foo, bar and baz be compared?" "Foo, bar and baz can be compared using the Kwyjibo algorithm, or by simply comparing their relative weights."

On a side note, I would always use "and" between the last two items in a list: "foo, bar and baz" instead of simply "foo, bar, baz". I don't know if there is a strict rule for such lists, but I find that the "and" reads better because I would always say it that way if I were speaking instead of writing.

  • 3
    Good answer, and let me reinforce that one needs to use and in a list of items. Additionally, the first sentence given in the question uses does ... can, which is wrong in that one would never use both in a verb phrase.
    – mgkrebbs
    May 8, 2011 at 18:20
  • @mgkrebbs: thank you, and good point about using does and can together.
    – e.James
    May 8, 2011 at 19:11
  • 2
    Nothings compares to foo! May 8, 2011 at 19:32

In modern English "do" is obligatory for forming negations and questions, unless there is an auxiliary verb (or the substantive verb is "be", or for some speakers "have").

A passive is formed with the auxiliary "be", so it is not negated with "do":

"A, B and C are compared"
"How are A, B and C compared?" (Not "How do A, B and C be compared?")

If another auxiliary, such as "can" is used, the same thing happens, whether or not there is also a passive auxiliary:

"A, B and C can be compared"
"How can A, B and C be compared?" (not "How does A, B and C can be compared?")

On the other hand, it is common in speech to express passive meaning by the word "get", as in

 "A, B and C get compared"

but "get" does not behave like an auxiliary, and does require "do":

 "Do A, B and C get compared?" (not "Get A, B and C compared?").

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