Q: A Brazilian friend of mine is taking English language lessons in Rio. She used the term “in the mind” with her teacher and she was told that this usage was incorrect. I told her that her teacher was mistaken. Who is correct? Is “in the mind” correct English?
A: I see nothing wrong with “in the mind.” For example: “Pain is all in the mind,” or “Who knows what’s in the mind of a terrorist?”
But there’s another expression without the article: “in mind,” as in “That’s not what I had in mind.” Perhaps your Brazilian friend should have used “in mind” and didn’t need the article.
I’d have to know the context to tell whether your friend was using “in the mind” correctly.