This is a complicated one. There is fate, which says that certain characters will do certain things, but external forces can be reacted to. There is history, that controls major events and doesn't like to be messed with, but ignores the content of conversation... Screw it, I don't even understand it and I'm turning the rules on their ear anyway. The big question is Does it count as a circular answer if a character says "You should go ask X, he'll be Y today." The circular answer being that a time traveler handed someone the answer to a question that he actually had to work out. (You hand your math homework to yourself in the past to copy.... where do the answers come from?) I guess a better example is that you do a speech in front of the class, someone compares it to X book, and you go into the past and suggest that someone check in X book.