The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Yes, but you didn't portray her
as completely IRRATIONAL.
The Big Bang Theory Season 1, Episode 7

You know, Pythagoras had
an IRRATIONAL fear of beans.
The Big Bang Theory Season 9, Episode 10

I realize it's IRRATIONAL,
The Big Bang Theory Season 10, Episode 18

And an IRRATIONAL constant.
The Big Bang Theory Season 5, Episode 16