With Matt Smith’s regeneration on the horizon, I’ve been thinking a lot about the differences between Russell T. Davies (who ran the show during Christopher Eccleston and David Tennant’s runs as the Doctor) and Steven Moffat (who has run the show since Tennant passed the role onto Matt Smith).

SPOILERS for all the 9, 10, and 11th Doctors’ episodes.

The 10th Doctor says “allons-y” because the phrase came up in a conversation with Rose, and every subsequent use of the catchphrase invokes her memory to both the audience and the Doctor himself.

Everytime he uses it — in many different contexts — we know he’s thinking of the friend he lost, his loneliness, and his anger. He still hurts for having lost Rose, but he’s co-opted a phrase that could be incredibly sad and demoralizing and uses it as a weapon. He fights because he lost Rose, not in spite of the fact he lost Rose. Its use is simultaneously sad and uplifting.

The 11th Doctor says “geronimo” because it is his catchphrase.

We know it is his catchphrase because it is one of the first things he says.

When the 10th Doctor finds out he is going to die, he spends three separate episodes dealing with this knowledge.

Denial turns into rage turns into arrogance turns into megalomania turns into tragedy turns into regret turns into denial again. Even before we reach the episode where 10 finally does die, we’ve spent three hours watching him deal with the knowledge of his fate. We’ve seen it change who he is and drive his actions in ways that are not always good.

Nothing is particularly surprising about the 10th Doctor’s death, but in exchange for this lack of surprise we have experienced a great deal of deep characterization and drama.

When the 11th Doctor finds out he is going to die, he is a little sad.

In several interviews, Steven Moffat has also hinted that, due to various quirks of canon, Matt Smith’s Doctor is actually the thirteenth incarnation of the character. This means that, according to established rules of the franchise, Matt Smith’s Doctor could potentially be the last (as far as the character knows, at least).

We know this not because this information was brought to light at a relevant time in the story when its reveal could color the 11th’s Doctors thoughts and actions.

We know this because Steven Moffat said it in an interview two weeks before Matt Smith’s Doctor is set to regenerate.

This is a surprise, and Steven Moffat likes surprises.

When the 10th Doctor says “I don’t want to go,” it is sad.

As the final third of his last episode is seemingly about the 10th Doctor coming to grips with his death and accepting it (“I’ve lived too long,” he says shortly before sacrificing himself to save an old man), these final words are a vicious knife twist. Just when we thought 10 was okay with dying — had made peace with his friends and the mistakes he had made — his last words reveal that, above all, the 10th Doctor was characterized by a love of life and adventure. Not only that, his valediction reveals that no matter how alien or quirky or seemingly invincible he might have seemed, he still suffers from that same emotion that follows every human, every moment of their lives: fear of death. He will miss it all.

When Steven Moffat makes the 10th Doctor say “I don’t want to go,” it is a joke.

The 10th says it in an entirely unrelated context as he leaves the stage. The 11th Doctor then jokingly states, “he always says that.” The audience is asked to laugh at the memory of his death, but it is meant to be okay because after all it is just a catchphrase and catchphrases are fun (Geronimo).

The 11th Doctor fought terrifying monsters of many varieties.

The Weeping Angels horrified us through their imaginative logic: if we kept our eyes open and didn’t blink (something any child who has ever had a staring contest can relate to), they wouldn’t kill us. Not only is it very physically difficult to stare at something without blinking, it’s also that much more unnerving that the only way to survive death is to stare directly at the thing that wants to kill you. There is essentially nowhere to hide. The Silence were terrifying because the idea of forgetting — of having an entire experience erased from our memories — is something that inherently scares us all to varying degrees. These two monsters took some basic human fears and quirks, then turned them around on us.

The 9th Doctor fought farting aliens who took over Downing Street and tried to escape on a magical surfboard.

One of them says “I’m shaking my booty” right after she farts.

The 10th Doctor’s companions are flawed characters.

Rose was smart and eager but could also be extremely rude and selfish. She happily left her boyfriend behind so she could go on adventures without him, but she also risks her life to save him a handful of times and makes every effort to check in with him between adventures. She is torn between her love of travelling with the Doctor and her duty to her family and friends at home. She does not always handle this balance well, and often upsets the people she loves through her own actions. Every choice she made had a consequence that resulted in conflict and arguments with the other characters (whether with the Doctor over her choice to save her father from death, or Mickey over her choice to side with the Doctor, or her mom over her choice to keep travelling no matter what).

Martha was capable and sarcastic but emotionally immature. She initially could not deal with the fact that the Doctor did not reciprocate her affections and was often unsure how to deal with being, essentially, his rebound girl. Eventually she grew up and left him, but not until she’d already had her heart broken. Martha’s affections for the Doctor were central to her character arc, and the show never shied away from discussing them.

Donna was loud, arrogant, and obnoxious, but incredibly compassionate. She might yell at people or act like an unruly customer at a retail store when she didn’t get her way, but she always wanted to help people no matter the cost (see: The Fires of Pompeii).

The 11th Doctor’s companions are strong female characters.

Amy was strong, smart, capable and a little bit flirtatious.

Clara is strong, smart, capable and a little bit flirtatious.

Sally Sparrow was strong, smart, capable and a little bit flirtatious. And Carey Mulligan.

When Amy cheats on her fiancee by making out with the Doctor, it is mentioned exactly once and then forgotten entirely.

When Russell T. Davies ended a season, he answered nearly all questions and gave the characters personal dilemmas to deal with.

In “The Parting of the Ways,” the Doctor had to choose between sacrificing thousands of innocent lives (for the second time) and risking the chance that the Daleks might destroy the entirety of creation. Rose, meanwhile, had to choose between staying at home with her family where she would be safe, or disobeying the Doctor’s orders and running straight into a battlefield to save his life. We found out what “Bad Wolf” meant, even if the ultimate meaning was pretty stupid.

In “Doomsday,” the Doctor has to deal with the knowledge that Rose might die. This finale parallels the previous one, except this time Rose is the one who suffers the consequences. The Doctor and Rose finally put words to their feelings…almost. The Doctor lives to regret not telling Rose what he felt when he had the chance, and this regret and longing will stick with him throughout the rest of his life. We find out what “Torchwood” means, even if the ultimate meaning was pretty stupid.

In “Last of the Time Lords,” some really stupid shit happens with Gollum and Space Jesus and Peter Pan satellites, but the Doctor has to decide how to deal with a monstrous villain who is both his archenemy and the only other surviving member of his race. The Master, meanwhile, makes a choice that he’d rather die and in so doing “defeat” the Doctor than remain alive as his prisoner and potential friend. We found out what “Mister Saxon” meant, and the ultimate meaning was pretty important.

In “Journey’s End,” some really stupid shit happens and every character meets every other character and clones happen, but the Doctor has to choose over letting Donna stay with him but inevitably die, or wiping her memory to save her. He saves her life against her will, and he is pushed even deeper into depression now knowing that he has lost another friend.

In “The End of Time Part 2,” the Doctor has to make many decisions. Does he use violence against the Time Lords to save reality? Does he sacrifice himself to save an old man of no particular importance? Does he go quietly to his grave, or does he rage against the dying of the light?

When Steven Moffat ended a season, he made sure it was full of lots of surprises and questions.

In “The Big Bang,” Rory chooses to stay by his dying wife’s side for thousands of years. The Doctor almost dies but doesn’t by being clever. The entire episode was about the TARDIS exploding and creating cracks in reality, but we did not find out why the TARDIS exploded. But the Pandorica was built by the Doctor’s enemies to imprison him, which is surprising.

In “The Wedding of River Song,” the Doctor almost dies but doesn’t by being clever. We find out who River Song is and who the Silence are, but we do not find out why they want to kill the Doctor other than the fact that if he says his name bad things will happen. The Doctor and River Song get married, but The Doctor seemingly doesn’t want to and is brutally mean to River Song but does it because apparently they like each other. But the Doctor still gets married, which is surprising.

In “The Name of the Doctor,” the Doctor almost dies but doesn’t because Clara is clever. The Doctor sort of says his name, but nothing bad happens. We still do not know why his TARDIS exploded, or what will happen when he says his name. But it turns out Clara is simultaneously all of the Doctor’s companions ever, which is surprising.

Russell T. Davies structured Doctor Who around characters — how they felt, how they behaved, who they were, and how they changed. Sometimes his plots were really stupid.

Steven Moffat structured Doctor Who around puzzles, mysteries, and catchphrases. Sometimes his plots are really cool.