Is it of coarse or of course?

The spelling of the phrase meaning “certainly” or “obviously” is of course. It is also sometimes used in place of “you’re welcome” as a response to “thank you.”

“Coarse” means “rough” or “vulgar.” It is sometimes used with the preposition “of” to describe something’s texture (e.g., “This sack is made of coarse material”).

Of course is by far the more common phrase.

QuillBot’s free Grammar Checker can help you make sure you’re using phrases like of course correctly.