Ever since ... , I knew that you were different.
Hello. In an American movie, a member of an oversight committee says this to a scientist:
Ever since you walked into my classroom in your freshman year, I knew that you were different. Over the years, your genius has been most impressive. This committee has given you remarkable leeway. We've tolerated your personal eccentricities, as well as your need for privacy. And I assure you, our patience is running out.

I don't understand why he used the past tense in "Ever since you walked into my classroom in your freshman year, I KNEW that you were different." Could you explain to me why it is not "Ever since you walked into my classroom in your freshman year, I HAVE KNOWN that you were different.", please?

Thank you.

Question

Ever since ... ,  I knew that you were different.
Hello. In an American movie, a member of an oversight committee says this to a scientist: 
Ever since you walked into my classroom in your freshman year, I knew that you were different. Over the years, your genius has been most impressive. This committee has given you remarkable leeway. We've tolerated your personal eccentricities, as well as your need for privacy. And I assure you, our patience is running out.

I don't understand why he used the past tense in "Ever since you walked into my classroom in your freshman year, I KNEW that you were different." Could you explain to me why it is not "Ever since you walked into my classroom in your freshman year, I HAVE KNOWN that you were different.", please?

Thank you.

Answer

It's completely natural.  The story starts in the past and moves forward to the present in three steps.

The first time frame is the student's first year at university (with no reference to the present).  The text uses the simple past:  "Ever since, you walked into my classroom"... "I knew you were different." (knew is used as a synonym of recognized).

The second time frame is the period after university until the present.  The text uses the present perfect: "the committee has given" ... "we've tolerated."

The third time frame is the present.  The text uses the present simple and present continuous: "I assure you" ... "our patience is running out."

Answer

You are right that “I have known” would be correct and is technically better.  But this particular phrase — “I knew you were different” — is sort of a cliche or set-phrase.  It sounds correct to my ear, even though it is technically not the best tense to express the thought.  So, think of it as idiomatically correct.

Answer

I like Susan's explanation the best. I don't have anything against "I knew that you were different." on its own. It's the "since" that makes the whole sentence sound wrong to me. Can any AmE speaker back up her explanation, please?

Answer

I agree it should be "I have known". An alternative way of expressing the idea is "As soon as you walked inot my classroom [...] I knew you that you were different." I think the two structures have been mixed here, producing this unsatisfactory/ ungrammatical sentence. (British English native speaker.)

Answer

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