Originally Posted by Salford_Who:
“So basically you're saying its the chicken and the egg - but we do know what happened first, the doctor was trapped - it's a very poor plot device.”
Rubbish. The same logic would unravel the basic premise of "Blink," too. Sally could never have seen the Doctor's "easter eggs" if he hadn't already got the transcript of their "conversation" over the DVD.
Same could be said of "The Terminator." Whole story being a causal loop. Skynet sends back a Terminator to kill John Connor's mother, forcing the resistance to send back a saviour, who ends up being John Connor's father, who causes the resitance that defeats Skynet, who sends back a Terminator to kill John Connor's mother, forcing the resitance to send back a saviour...etc.
Self-contained causal loops, with no beginning and no end are a long-stanidng trope of time-travel fiction. It's proper sci-fi, playing with the "what if" scenario of people operating outside of linear time. If you consider that a "poor plot device" then sci-fi time-travel stories are not for you.