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Which of the following sentences are correct?

"It is you who have to update your opinions, not I."
"It is you who has to update your opinions, not I."

From what I've learned "has" is for singular. So if "who" is referring to one person, it should be "has". But this rule doesn't seem to be followed. I googled "it is you who have to" and "it is you who has to" and "have to" returned 6 times as many results. Of course, "you" can be plural, but in the majority of sentences it was referring to a singular person.

I my ears, "who has" or "who have" both sound fine in all cases and it seems like people don't care which one they use.

So..

1: What is grammatically correct?
2: What is colloquially correct?
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Here is my take on it. (I'm a veteran poster, but not on this forum, if that matters. I like to let my posts speak for themselves.) Native speaker have trouble with this construction.

The "not I" rules out colloquiality. "I" in that place is extremely formal. "Not me" is usual, whatever the grammar of it. But that is not the question here.

"Who" takes the number and person of its antecedent. That is not always borne out in practice, but even the worst of us at least feel a little uneasy about our selection of conjugation after "who" even when we happen to be right, so you might as well be right. Sound grammar makes it, "It is you who have to update your opinions, not I", because you have to, and if it had been "he", it would have been, "It is he who has to update his opinions, not I", because he has to.

The technically ungrammatical "you who has" comes from a tendency to give up and default to the traditional generic masculine third person "he" when the grammar gets gnarly. You hear it both ways, and it isn't a very jarring mistake. Most people don't think that hard about it, and the meaning is clear either way.
Comments  
Yes, you are right: many native speakers do not care too much about this matter,

This is what I have learned. (If any of the veteran posters disagree with my opinion, you must accept their answers as the correct ones, not mine.)

Yes, grammatically speaking, the "correct" answer is:

It (who has to update his/her opinions) is you, not I.

BUT over the years, native speakers have decided to make the verb agree with the subject complement:

It is you (subjective complement) who have (agrees with "you") to change your opinions, not I.

Here is another example that I have made up:

It is I who am very interested in the adverb "really." (In theory, it should be "It is I who is interested ....")

HAVE A NICE DAY!
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Verb agreement in this sentence: "It is you who know/knows..."

Question
Vanessa from the Philippines asked: Which is correct, “It is only you who know my secret,” or “It is only you who knows my secret”?

Answer
This is a difficult question to answer, because both of these constructions are used by native speakers, and there are good arguments to be made for both.
The argument for using “It is you who know…” comes from more traditional grammarians who tell us that the verb in a relative clause beginning with who should agree with the noun that who represents. In the sentence, "It is only you who know my secret," who represents the pronoun you, which takes the 2nd person form, know.
However, most native speakers would use “It is you who knows…,” because the combination who + know, with a 3rd person pronoun and a 2nd person verb, seems odd and wrong.
Given this conflict, my advice would be to rewrite the sentence as “You are the only one who knows my secret,” and avoid the question completely!

I hope this helps.
 enoon's reply was promoted to an answer.

Who has

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