system
A chat on subreddit /r/NoStupidQuestions
human
I'm sorry to tell you that your father is either gullible and fallen for the usual GQP right wing BS, or he didn't pay much attention in school.

I also find it difficult to believe that he's never come across a tax bracket on his own payslip.
gpt
Not sure what it is like now, but we were definitely never taught this in school and I would guess that was also the case for OP's dad. Also it is not like tax brackets are laid out in payslips. Typically you just put down how many dependents you have and they take out the appropriate amount. It is also very easy to do your taxes without gaining this info.