10 Times Doctor Who Has Broken Its Own Rules

Time travel is tricky, and rules have to be obeyed. One of the revival series' first instances of this was Father's Day when the Ninth Doctor warned Rose Tyler not to cross her personal timeline, not to change the past, and certainly not to interact with other versions of herself.

When Rose held a younger version of her, the time-feasting Reapers managed to cause chaos - even devour the Doctor. This proved that timelines shouldn't be messed with. However, this rule didn't seem to apply to Kazran Sardick or Amy Pond who met versions of themselves in 2010, or even when Amy interacted with a future version of herself in The Girl Who Waited.

Crossing timelines were also dealt with in 2015's Before The Flood, and the Twelfth Doctor had to be very careful not to change history - even if it meant not saving a life.

Even interacting with other regenerations is meant to be impossible, or at least very dangerous, according to the Doctor. Episodes such as The Day of the Doctor explained why the characters could meet in-narrative, but Twice Upon A Time failed to reason why two Doctors could occupy the same adventure. Likewise, no explanation is given as to why two incarnations of the Master could meet, dance, and kill each other in 2017's World Enough and Time/The Doctor Falls.

With the number of paradoxes and wounds in time occurring throughout NuWho, you would think the Reapers would be on hand a bit more often.