Kerotski read the letter, and a look of relief came over his round face. "Not the same typewriter or paper, but this is him, all right. What more do we know?"

"Plenty. Hold on, and I'll give you a complete rundown." He picked up the telephone and began speaking in a low voice. It was an ordinary-sounding conversation; even if the wire had been tapped, no one who was not a "core" member of the S.M.M.R. would have known that the conversation was about anything but an esoteric article to be printed in The Metaphysicist—something about dowsing rods.

The core membership had one thing in common: understanding.

Consider plutonium. Imagine someone dropping milligram-sized pellets of the metal into an ordinary Florence flask. (In an inert atmosphere, of course; there is no point in ruining a good analogy with side reactions.) More than two and a half million of those little pellets could be dropped into the flask without the operator having anything more to worry about than if he were dropping grains of lead or gold into the container. But after the five millionth, dropping them in by hand would only be done by the ignorant, the stupid, or the indestructible. A qualitative change takes place.

So with understanding. As a human mind increases its ability to understand another human mind, it eventually reaches a critical point, and the mind itself changes. And, at that point, the Greek letter psi ceases to be a symbol for the unknown.

When understanding has passed the critical point, conversation as it is carried on by most human beings becomes unnecessarily redundant. Even in ordinary conversation, a single gesture—a shrug of the shoulders, a snap of the fingers, or a nose pinched between thumb and forefinger—can express an idea that would take many words and much more time. A single word—"slob," "nazi," "saint"—can be more descriptive than the dozens of words required to define it. All that is required is that the meanings of the symbols be understood.

The ability to manipulate symbols is the most powerful tool of the human mind; a mind which can manipulate them effectively is, in every sense of the word, truly human.

Even without telepathy, it was possible for two S.M.M.R. agents to carry on a conversation above and around ordinary chit-chat. It took longer, naturally; when speaking without the chit-chat, it was possible to convey in seconds information that would have taken several minutes to get over in ordinary 

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