Ever since River Song first graced fans with her presence in the Tenth Doctor's Silence in the Library/Forest of the Dead two-parter, people knew that she was going to be an odd one. Here you have a Time Lord, master of space and time, meeting a woman who knows him, knows his biggest secret, and has a futuristic version of his sonic screwdriver, yet he has no blooming idea who she is... And it would take fans a few more series to fully understand the confusion behind River Song, and how she is seemingly travelling in the opposite direction to the Doctor. But is it really that simple? Well, no, apparently. Her timeline, with respect to his, is really like that big ball of timey-wimey stuff that the Doctor referred to in Blink. In the Series 5 episode The Time of Angels, for example, River Song isn't a professor, however, in Series 6, she is... or was at least enrolled in courses to become one. If she's travelling backwards to the Doctor, she should already be a professor by this point, as she is already in prison for killing the Doctor... Unless she was just lying the whole time. Secondly, the episode Let's Kill Hitler, in which Mels regenerates into River Song, should in theory end all of River Song's appearances, if they truly are travelling backwards to each other. Yet River Song still meets up with the Doctor and companions a few more times between Series 6 and 7. If she was able to meet up with the Doctor then, why did she have to be a computer generation in The Name of the Doctor, and not her normal self? While her timeline mostly seems to travel backwards with respect to the titular Time Lord's, there are times where they are seemingly experiencing things at the same time. That's bound to put less strain on their relationship, for sure!