A Horse Is a Horse, Of Course, Of Course

Of course there are phrases that need to be set off by commas. However, "of course" isn’t necessarily one of them (out of neglect or habit writers often add the comma no matter what). If you intend "of course" to mean “by the way” or “as a matter of fact,” use a comma, as when Rudyard Kipling said “words are, of course, the most powerful drug used by mankind.” Skip the comma if you intend "of course" to act as an emphatic. “Of course I’ve played outdoor games,” Oscar Wilde told a friend. “I once played dominoes in an open-air cafe in Paris!”