Is "which" omittable in this sentence?

Question

I wrote a sentence in an assignment, which is something like: *"The magazine has a vocabulary of 4,000 to 7,000 words, which is the same as that the GSAT requires."

My teacher, who is a native speaker of English,corrected it by putting the relative pronoun "which" back in the clause "the GSAT requires."

(The GSAT stands for General Scholastic Ability Test. It is the exam every 12th grader in Taiwan has to take for college application.)

While I was making the sentence, I first made three sentences:

1. The magazine has a vocabulary of 4,000 to 7,000 words.
2. The vocabulary of 4,000 to 7,000 words is the same as the vocabulary of 4,000 to 7,000 words.
3. The GSAT requires the vocabulary of 4,000 to 7,000 words.

Next, I combined sentence 1 and 2 using the relative pronoun "which" and the demonstrative pronoun "that," as in: "The magazine has a vocabulary of 4,000 to 7,000 words, which is the same as that."

Finally, I combined this complex sentence with sentence 3 by replacing "the vocabulary of 4,000 to 7,000 words" with the relative pronoun "which" and by using it as a conjunction to set off the relative clause, as in:

"The magazine has a vocabulary of 4,000 to 7,000 words, which is the same as that which the GSAT requires."

Here is my question: I think of "the vocabulary of 4,000 to 7,000 words" in sentence 3 as the object of the transitive verb "requires." It is my understanding that a relative pronoun, such as "whom" and "which," is omittable when it is an object of a verb or preposition, so I opted not to write "which" when I constructed my sentence. However, my teacher doesn't seem to think so.

I did go to ask her why but failed to get a straight answer from her. I did some research online but found few, if any, discussion threads on this topic. And they mainly focus on the meaning of the construction "that which" used together. I want to know why "which" can't be dropped in this construction even though it is an object of a verb. I'd appreciate it very much if you would tell me what you think. Thank you very much!

Answer 1

Looking first at your three individual sentences.

No 1. is fine.

No 2. makes no sense. To say that the vocabulary of x words is the same as the vocabulary of x words is like saying that two is the same as two. What you mean is that the (magazine's) vocabulary of 4,000 to 7,000 words is what the GSAT requires. Or, meets the GSAT's requirements.

No 3. needs to be changed from the vocabulary to a vocabulary, although you are intending to refer back to the magazine's vocabulary.

The simplest way to convey your meaning is to write: The magazine's vocabulary of 4,000 to 7,000 words meets the GSAT's requirements.

If you intend to combine your three sentences, using which you might say:

The magazine has a vocabulary of 4,000 to 7,000 words, which (is what) the GSAT requires.

If you wanted a construction closer to your original, you might write: which is the same as that required by the GSAT, although this just uses more words to say the same thing.

To use a complicated unnecessary construction such as the same as that which (meaning **the same number as the number that/which the GSAT requires) is simply clumsy and word heavy.