You absolutely can jam over a song you don't know inside and out. If everyone did know the song that well then you're just playing the song. Real "jamming" (not

You absolutely can jam over a song you don't know inside and out. If everyone did know the song that well then you're just playing the song. Real "jamming" (not trying to be too pedantic with the use of the word) happens when you don't know where the song/jam is going and you build off of and comp each other.