He'd considered using John Smith -- after all, his other self had used
the name many, many times. It was his fallback to humanity. Precisely
why, he reasoned, he ought not to use it. When it came down to it, John
Smith was him -- so was he, but John Smith was too much a part of
his other self. Too much of a reminder. Not as if his very being
wasn't the biggest reminder in any universe. Still, John Smith had been
his...and he wanted something of his own. He went over a few
names in his head -- Jack, Jamie, Mickey...every name seemed to be
connected with the life he'd left -- no, the life he hadn't really
lived, but remembered as if he had. Not an easy separation, but
necessary, if he was going to truly be able to give Rose everything she
needed.

He went through the alphabet. "Adric? Ben? Umm...C? No, no
C's...David?" He'd always rather liked that name. "Good, strong, manly
name, is David!" Common enough, he thought, remembering Proper Dave and
Other Dave he'd met at the Library, before the darkness... He tried it
out. "David...David Smith? Nope, don't like how it feels rolling off
the tongue like that. What about David Jones?!" Thoughts of dead
pirates and bubblegum pop songs filled his head, leaving him vaguely
nauseous, though thoughts of Martha made him smile, albeit a little
sadly. No, Smith and Jones were out. Then it came to him. "Noble.
As in Donna Noble -- for one brief, shining moment, the most important
woman in the universe, and why not? She'll never know...but I will, and
I want to always remember, as much as she can never... After all, she is
a part of me. David Noble. Doctor David Noble! Yes! That
suits. To a "T". Well, a "D", anyway..." He went straight away to
tell Rose, Pete and Jackie his decision.