Certain Knowledge

SPOCK: We cannot return him to Earth, Captain. He already knows too much about us and is learning more. I do not specifically refer to Captain Christopher, but suppose an unscrupulous man were to gain certain knowledge of man's future? Such a man could manipulate key industries, stocks, and even nations. and in so doing, change what must be. And if it is changed, Captain, you and I and all that we know might not even exist. KIRK: Your logic can be most annoying.