"Books which cost half price are sold quickly"

Can anyone explain to me please why "book" in this sentence is the subject? And why it is not the object?

  • 1
    What's being sold? The books. Hence they are the subject
    – kos
    Commented Jul 22, 2015 at 14:12
  • Explaining it a little better (wait for a proper answer tough, I'm not a native speaker): "Books which cost half price are sold quickly" is a passive form, hence the subject and the direct object are switched compared to the relative active form; nonetheless what would be the subject in the relative active form is implied; a possible active form would be "[The] [subject] sell[s] the books which cost half the price quickly", I think your confusion arises from this
    – kos
    Commented Jul 22, 2015 at 14:30
  • In your sentence: "[Books which cost half price] are sold quickly", the subject is the noun phrase "Books which cost half price".
    – F.E.
    Commented Jul 22, 2015 at 18:56

3 Answers 3


The phase "which cost half price" is just something that describes "books". It is an "adjective phrase." Look at it like this: Books (which cost half price) are sold quickly.

(subject)    (adjective phrase)       (verb)     (adverb)
Books       which cost half price    are sold    quickly.

(I also agree with smjpilot that "that" should replace "which" in this sentence.)

  • I implore you to reconsider your final parenthesis--see my Comment on smjpilot's Answer. It does our learners a disservice to perpetuate such arbitrary "rules". Commented Dec 3, 2015 at 15:54
  • @StoneyB if the purpose of this site is to help people learn to use English and speak as much like a native speaker as possible, then they probably want to know those "arbitrary rules". And I didn't mean that "which" was incorrect, just that "that" was a better choice in this case.
    – jfren484
    Commented Jul 13, 2016 at 2:04

Books which cost half price are sold quickly.

The clause books which cost half price is employed as the subject of your example sentence. This subject clause has its own subject which is books.


Books which cost half price are sold quickly.

'Which' would be used to provide additional information about books, not to distinguish some books from other books.Since the 'cost half price' is an important part of the meaning, the sentence should be constructed as:

Books that cost half price are sold quickly.

The verb in this sentence is to sell, and the verb is applied to the books, so the books are technically the object of the sentence, as well as a subject. The passive voice emphasizes that the important idea is about the object, and the subject (the bookseller that would be involved if the sentence was constructed using the active voice) is not even mentioned.

  • The "rule" that only that and not wh- relatives should be used for restrictive relative clauses is an out-of-thin-air invention of late 19th-century grammarians which has never been generally accepted or followed by even the most punctilious writers. Commented Dec 3, 2015 at 15:51
  • Who is the most punctilious writer?
    – smjpilot
    Commented Jun 8, 2016 at 18:51
  • Robert Graves was right up there. Commented Jun 8, 2016 at 19:07

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