have vs had (Things have changed because something happened to him exactly...)

[Tweak]

dear teachers,

Things have changed because something happened to him exactly two years ago.

why use have instead of had? isn't the sentence a past tense?

thanks!

tweak

[Mister Micawber]

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Yes, but both 'have' and 'had' work in the past. 'Have' because the speaker refers from a past point up to now.
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Native English teacher at Mister Micawber's