선생님 or 선생
I understand that the 님 'nim' is an honorific ending. Would you use it no matter what? I found this sentence in a lesson online:
그 선생님은 좋아.

Would 그 선생는 좋아 be the same meaning? Do I need the 님 at all times?

Question

선생님 or 선생
I understand that the 님 'nim' is an honorific ending.  Would you use it no matter what?  I found this sentence in a lesson online:
그 선생님은 좋아.

Would 그 선생는 좋아 be the same meaning?  Do I need the 님 at all times?

Answer

You already explained  "님" is honorific expression.
"그 선생은 좋아" is also a proper sentence. If you are older than "그 선생" or of the same age, you don't need to add "~님".
But sometimes people add "~님" to show respect, even though  "그 선생" is younger or of the same age.
The most safe way is adding "~님" regardless of age.