Who's that book by? vs. Whom's that book by?

Which one is more spoken by native English speakers?

Which one is more written by native English writers?

In terms of grammar, in the past, only 'whom' was accepted as a correct form — by whom(objective case of 'who')

  • 1
    I was about to write a detailed Answer, when I noticed that 635 Questions on ELL contain "who or whom" - ell.stackexchange.com/search?q=who+or+whom Please, how many, if not specifically which of those went into your research? May 11 at 18:49
  • 1
    A proper rearrangement would be, "That book is by whom?" (correct use of object, with him replaceable for whom) Leading to a response of, "That book is by him."
    – killermist
    May 12 at 23:00

5 Answers 5


Who's that book by?

is 100% natural and common.

Whom's that book by?

I've never heard it, and it sounds terrible to me, though I suppose technically the grammar is good.

Whom is that book by?

Without the contraction, it sounds OK, but is not common at all. It sounds overly formal or stuffy.

  • 24
    Or "By whom is that book?" (If the test writer want you to use whom, they also probably don't want to end in a preposition)
    – James K
    May 11 at 5:39
  • 7
    @BEBYGONES It's a question of acceptable to whom. Except in certain circles, the use of whom in the English language is dying. It's now idiomatic, if not actually correct, to follow a preposition with who. Sadly! May 11 at 8:33
  • 4
    @BEBYGONES google ngrams does show "by whom" as more common than "by who" even in the fiction corpus (which is likely to be more idiomatic than non-fiction) although the gap has closed enormously over the past century. I tried a similar comparison for "who is it by", "who's it by" and "whom is it by", but the latter had too few hits to appear books.google.com/ngrams/…
    – Tristan
    May 11 at 16:08
  • 10
    Contracted or not, "Whom is that book by?" should not sound OK. Much more than merely "not common at all, overly formal or stuffy" it's simply wrong. In that context we always need "By whom…", we should never use "Whom by" and no, "Whom is that book by?" doesn't change anything. May 11 at 18:38
  • 3
    @RobbieGoodwin Nonsense. Unlike "whom" in the oblique which is a feature of English which is becoming increasingly archaic, the "rule" that a preposition cannot be separated from its object is something intentionally imported from Latin that never really caught on. They are unrelated except in the fact that they are both pet peeves of the most pedantic sort of prescriptivists. May 12 at 9:07

The simplest way to ask that question is:

Who wrote that book?

The original "Who's that book by?" is a clunky, unnatural construction. You've got the who/whom thing going on as well as the often maligned "ending a sentence with a preposition."

"Who wrote that book?" is simple and direct. It is clear and natural. It's the way I (as a native English speaking person) would say it.

  • 8
    to me it sounds natural enough with a pronoun (e.g. "who's it by"). If my friend was talking about a book they were reading, and I wanted to find out its author, this would seem more natural to me than saying "who wrote it". Otoh, if I were pointing at a book in a shop or library and asking about its author I agree that "who wrote that book" is more natural
    – Tristan
    May 11 at 16:11
  • "Who wrote that book?" transforms to "He wrote that book." quite naturally. And the ending on a preposition is also a problem because a preposition is a pre-position. It expects a position. And further "Who's that book by?" (adding a position) naturally gets strange as "Who's that book by the duck?" "Who wrote that?" (dropping the object book as implied) is also valid and natural. "Who's wrote that?" or "Who is wrote that?" would cause me to cringe if heard in conversation if not done to intentionally sound wrong. (which I intentionally do sometimes)
    – killermist
    May 12 at 22:47
  • -1: I (native UK English speaker) would always use "Who's that book by?" and it would be perfectly understood by everyone I know. I would likely never use "Whom's that book by?" unless I was trying to sound deliberately over-correct. May 13 at 16:24
  • 1
    @Tristan Agreed, "Who's it by" sounds fine. If someone wants to be more formal, "By whom?" would be the construction that avoids ending a sentence in a preposition and correctly uses the objective rather than subjective form of the author. May 13 at 19:33

My school (in rural Australia) never once even mentioned that there were times that "whom" would be a better choice of words, but as I started to encounter the word in the wild I figured out a fairly practical test for use in my own writing: replace "who" with "he" and "whom" with "him" to form a sentence that looks like an answer, and see which version of the answer makes sense.

  • "Who wrote the book?" => "He wrote the book."
  • "Whom wrote the book?" => "Him wrote the book."
  • "By who was the book written?" => "By he was the book written." (or "By he the book was written.")
  • "By whom was the book written?" => "By him was the book written." (or "By him the book was written")

The second and third of those examples both stand out as wrong to me.

The interesting thing about this question is that both "He's that book by" and "Him's that book by" both seem wrong. If I found myself writing or speaking in the sort of situation where I thought my audience would take note of "who" vs "whom" and needed to ask the question I'd very likely rephrase it to one of my "good" examples from above.

It's also my experience that a relatively small portion of my audience will even notice a "who" that should've been a "whom", and a tiny subset of those will object to it. It's probably more common to object to a "whom" that should've been a "who" than the reverse. In that light, "Who's that book by" is your best bet. If in doubt, leave it out!

  • 6
    Note that the awkwardness of "him's that book by" is primarily one of word order - change it to "that book is by him", and it sounds natural. That suggests "that book is by whom" as a valid alternative; and indeed the kind of formal/old-fashioned grammar that requires "whom" would probably object to the trailing preposition as well.
    – IMSoP
    May 12 at 11:37

I think there's a few things going on here...

Whom's that book by?

The contraction "whom's" sounds odd, because "whom" is now generally used in formal contexts, and contracted "is" in informal contexts.

Whom is that book by?

Next, the word order makes it hard to see which is the subject and object in the sentence. If we switch that around, it becomes clearer that the subject of "is" is "that book":

That book is by whom?

As Teaspoon's answer points out, you can usually substitute "he" for "who" and "him" for "whom". In this case we could answer the question like this:

That book is by him.

This suggests that "whom" is indeed correct. But what about the word order? Let's compare a different phrasing:

The book is by which person?
The book is by that person.

The question is understandable, but doesn't sound natural, because we generally rearrange the word order to make a question:

Which person is the book by?
The book is by that person.

(Some grammarians would object that the preposition should not end the sentence, but there is little evidence that natural English has ever followed such a rule.)

Put together, that suggests that the technically correct form is:

Whom is that book by?

However, as others have noted, the use of "whom" in English is declining, so in an informal context, as implied by the contracted form, it would probably be:

Who's that book by?

  • Technically 'Whom is that book by?' But modern native speakers say 'Who is that book by?' I guess this may or would cause, in the future, 'by+subjective case' to be widely used: by who
    May 12 at 12:44

Only whom was accepted as correct when it was the object of the verb. ("Whom were you speaking to?")

Here, who is the subject ("Who is the author of the book?"). It would never have been correct to use whom in this context.

  • 4
    'whom' is the object of the preposition 'to' and 'who' is a complement and 'the author' is a subject. 'who' is an interrogative pronoun. See this: Who are they? Who is he? and see this: Who made this box?(here who is a subject that made this box)
    May 11 at 11:14
  • 1
    Precisely - nobody would ever have said Whom is he? etc. May 11 at 11:58
  • 4
    I'm a little confused, because "Who is the author of the book?" is not mentioned anywhere in the question (in fact, the word "author" isn't mentioned anywhere in the question), and I don't see any changes in the edit history. I guess that I'm missing something. May 11 at 16:06
  • 3
    But in the question "Who's that book by," the subject is "that book," and the word "who" is the argument of the preposition "by," not the subject. May 11 at 16:54
  • 2
    "Who(m) is it by?" is short for "Who(m) is it written by?", which is the passive voice version of "Who wrote it?" So while the author is in reality performing the action of writing, grammatically, the passive voice makes them an indirect object. May 11 at 21:01

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