of course

We use of course (not) to mean ‘as everybody knows’ or ‘as is obvious’.

• It looks as if the sun goes around the earth, but of course that’s not true.
• We’ll leave at eight o’clock. Granny won’t be coming, of course.

Of course can be used as a polite reply to a request.

• ‘Could you help me?’ ‘Of course.’

But of course is not always a very polite reply to a statement of fact.

• ‘It’s cold.’ ‘It certainly is.’ (not Of course it is. – this would suggest that the first speaker had said something too obvious to be worth mentioning.)

note

For the use of of course to structure arguments, (see here), (see here).