A human being is the sum of his/her memories. A Time Lord is even more so sccording to 5 in "The Five Doctors". Just to point out a couple of instances; while holding the dying Master in his arms, 10 reflects (almost nostalgiclly) about their past adventures, ie, the Axons, the Daleks, etc. Ten also recognizes Sara Jane in "School Reunion". In "The Five Doctors" 5 recognizes Susan Foreman (Campbell) as her Granddaughter although the memory seems hazy to him.
Time Lords retain their memories and experiences through regenerations. The personality behind the knowledge changes along with the face,The same memories, the same drive, mostly the same interests, pretty much the same person. He retains the same memories and basic personality, but w/ every incarnation comes different quirks and abilities. Like he will always be smart, passionate, and a little mad. But the current doctor is also very child like, a unique characteristic.I've pondered this question many times. My answer is the blue box. No joke. A. It's the only character throughout the entire series saving the Doctor himself. and B. The Tardis recognizes the Doctor as the same man so therefore at the core he must be. He's been alive or a long time and has gone through some drastic personality changes, but who hasn't? How many adults can say they're exactly the same kind of person they were when they were a teenager? How many would actually WANT to admit to that? How many teenagers can say they're exactly the same as when they were in Pre-K? the Doctor goes through life changing experiences but as his time goes on he changes gradually as one regeneration and consolidates that change easier than a typical man would through the traumatic experience of regeneration.Every cell is different, as is his face, his form and his personality. But he still has the same memories and it's sort of established that he's still the same man you can trust.It's the particulars of each incarnation of the Doctor that are different, not the man beneath it all. Does he like celery? Carrots? Bow-ties? All of these questions are surface questions, not really relevant to the character beneath. Because whether he wears a twenty-foot long scarf or a leather jacket, the man beneath the clothes is the same. An adventurer, a wanderer, a hero when at all possible, and always in a state of wonder at the marvelous universe we all live in, and anxious to point it out.
The truth is, we aren't our clothes, our mannerisms, or our faces. We are a driving spirit beneath it all, and the things that spirit consistently does, regardless of where it finds itself. And in that respect, the Doctor is always exactly the same.They all have the same memories and basically the same moral compass.To the extent that they share the same memories and core values. Other than that, they are completely different individuals. This was implied on several occasions by the 10th ("might as well be a different person") doctor, and once or twice by the 11th, and illustrated best from the transition from 10th to 11th, in that the 11th doctor had to re-learn various aspects of his anatomy (think Fish Fingers and Custard). Simple answer: Memories.
Even the new incarnations different reactions to a given situation can be seen in the different ways humans will react depending on age and experience.According to me, the Doctor is like different people who share the same memories. They have the same experience and knowledge but different minds that use them. The answer depends on your point of view :)
What makes us who we are... Personality, temperement etc... Is mostly a result of our own life experiences - how we are nurtured and how we experience the world (or universe). Because each incarnation of the Doctor has these same memories then the Doctor's personality reamins largely intact... The body however is not the same man. Every single cell has transformed so physically nothing remains of the previous incarnation. If you copy the contents of your harddrive from one computer to another, it doesn't change the data that is transferred. If it is indeed 'the soul' that is created by these experiences, then, although the memories have to be assimilated in to a different brain (which accounts for the small changes in personality) the Doctor lives on in a completely different body.
It's the old Ship of Theseus problem. Take a ship. Replace every plank of wood one by one, over a decade. New mast, new rigging, new crew and captain. Is it still the same ship? Maybe not, but at what point did it stop being the original ship - when you replaced the first plank? The second? Was it the mast? Regeneration is just this, sped up - the core, the essence, the bright spark that makes the Doctor the Doctor, remains with each regeneration. 22.214.171.124 02:51, August 8, 2011 (UTC)
I would agree that at his core the Doctor is the same man, and if nothing else his life experience and memories do transfer with each regeneration. I'd add that I don't take the regens to be a flick of the switch, brand new man sort of deal, either. I think you can trace certain personality traits through the Doctor's years and his growth, and that the personality that comes with a new Doctor doesn't come from no where, but is informed by his prior character. So in that way it is a lot like anyone who goes through a change of personality, only the Doctor's tends to be a bit more exaggerated and sudden which is part (along with his change in appearance) of why this question comes up. But as the person above said, we don't expect people to stay the same their whole lives, but since we are going through time at the same rate and spend so much time with them, these gradual changes don't stand out. Think of the Doctor's regen like a really good friend that goes away for six years without a word. When they come back, they might act like an entirely different person, but there is no question they are still the same individual. Just a greatly changed one.
As Steven Moffat has repeatedly pointed out in interviews, etc., there have not been eleven Doctors; there have been 11 incarnations (so far) of one Doctor.
Additionally, from the perspective of other Time Lords, regeneration amounts to getting a facelift. In "The Deadly Assassin", Runcible recognizes the Doctor from school and then a few moments later asks if he's had a "facelift", to which the Doctor responded, "Several". He only had a vague recollection of the Doctor's troubles with the Council, so it's likely he hadn't seen him since some time during his first incarnation. It's like when someone gets their hair done. Sometimes you notice something's changed, but can't pinpoint what? It seems like a big change from a human perspective, but much smaller from a Time Lord's.