5. Catchphrases
Catchphrases for the Doctor are in and of themselves a sort of in-joke. It is a malleable tool for self-reflexive humour and also, a marker of an era. But the potential contender for first ever catchphrase of the Doctor, the classic "reverse the polarity of the neutron flow" is already an in-joke. Apparently, Jon Pertwee suffered from an inability "to remember the gobblity-gook", according to Peter Davidson in Doctor Who Confidential Weird Science. This "gobblity gook" or "technobabble" as others called it, was the psuedoscience filled with complicated (and often made-up) words about whatever the Doctor was supposedly doing. This oft spoken phrase of the Third Doctor, is a result of one day's filming when Mr. Pertwee's lineswritten on a set he was not currently inwere temporarily unavailable, he used the only line he had memorised, and it stuck, so he kept using it. Apparently the idea of the Doctor with a catchphrase is a good one because it has become quite a staple of the show since this, earlier, almost accidental introduction.
The importance of catchphrases was noted in the Eleventh Doctor story, the Almost People, which featured a clone copy of the Eleventh Doctor in the midst of his own sort of regenerative crisis. He rattles off: "I've reversed the polarity of the neutron flow." Followed by the Fourth Doctor's catchphrase: "Would you like a jelly baby?" And the Sixth's: "Why?" And the Tenth's: "Hello. I'm the Doctor." Before mangling them all into: "I've reversed the jelly baby of the neutron flow. Would you like a Doctor, Doctor, I'm, I'm the. I can't."