Poetry, physics, the same thing.

The Doctor

Bill: What good’s getting in a box gonna do?!
The Doctor: What an extraordinarily long and involved answer this is gonna be!

Bill: It’s like a…
The Doctor: Spaceship!
Bill: Kitchen!
The Doctor [taken aback]: ...A what?
Bill: A really posh kitchen!

The Doctor: This is the gateway to everything that ever was and ever can be.
Bill: ...Can I use the toilet?

At this moment in time, Ruby Sunday, you are the only music in the world. Now let's see what happens when you bring music back.

Doctor: We have to hide.
Ruby: You never hide.
Doctor: I can't fight this thing.

The Doctor: I told you when I met you, fighting the Toymaker took everything. He tore me in half.
Ruby: But you survived.
The Doctor: He literally tore my soul in half. I can't survive that again.

You don’t “steer” the TARDIS! You *negotiate* with her! The still point between where you want to go and where you need to be. That’s where she takes you.

The Doctor

Nardole: Excuse me? What *is* the TARDIS doing down here?
The Doctor: I’m over two thousand years old. I don’t always want to take the stairs.

Nardole [sees Bill]: Why is she here?
The Doctor: Because she isn’t anywhere else.

Bill: So. Back up to your office for a cuppa, then?
The Doctor: Between here and my office, before the kettle boils, is everything that ever happened or ever will!

The Doctor: Okay. I suppose I owe you an explanation. A long time ago, a thing happened. As a result of the thing, I made a promise. As a result of the promise, I have to stay on Earth.
Bill: Guarding a vault.
The Doctor: Guarding a vault!
Bill: Well, you’re not guarding the vault right now.
The Doctor: Yes, I am! I have a time machine! I can be back before we left!

Doctor Who Quotes

There's a horror movie named Alien? That's really offensive. No wonder everybody keeps invading you.

The Doctor

The Doctor: It's a risk.
Graham: Oh, like none of our other trips have ever been risky.
The Doctor: I have apologized for the Death Eye Turtle Army! Profusely.