The Grand Design.

Sir Humphrey: "With Trident we could obliterate the whole of Eastern Europe."
Jim Hacker: "I don't want to obliterate the whole of Eastern Europe."
Sir Humphrey: "It's a deterrent."
Jim Hacker: "It's a bluff. I probably wouldn't use it."
Sir Humphrey: "Yes, but they don't know that you probably wouldn't."
Jim Hacker: "They probably do."
Sir Humphrey: "Yes, they probably know that you probably wouldn't. But they can't certainly know."
Jim Hacker: "They probably certainly know that I probably wouldn't."
Sir Humphrey: "Yes, but even though they probably certainly know that you probably wouldn't, they don't certainly know that, although you probably wouldn't, there is no probability that you certainly would."