Doctor: Once a man fell asleep and dreamt he was a frog. When he woke up, he didn't know if he was a man who dreamt he was a frog or a frog who was now dreaming he was a man. - SNAKEDANCE.
Doctor: Well, there's a probability of anything. Statistically speaking, if you gave typewriters to a tree full of monkeys, they'd eventually produce the works of William Shakespeare. - MAWDRYN UNDEAD.
Doctor: And if anyone happens to ask whether I made any material difference to the welfare of this planet, you can tell them I came and went like a summer cloud. - FRONTIOS.
Doctor: It's all right for you, Peri. You've only got one life. You'll age here in the TARDIS and then die. But me, I shall go on regenerating until all my lives are spent. - VENGEANCE ON VAROS.