Kraybo was twenty-one, and had been in training as a Guesser ever since he was old enough to speak and understand. He showed occasional flashes of tremendous ability, but most of the time he seemed—well, lazy. And then, there was always the question of his actual ability.

A battle in the weirdly distorted space of ultralight velocities requires more than machines and more than merely ordinary human abilities. No computer, however built, can possibly estimate the flight of a dodging spaceship with a canny human being at the controls. Even the superfast beams from a megadyne force gun require a finite time to reach their target, and it is necessary to fire at the place where the attacking ship will be, not at the position it is occupying at the time of firing. That was a bit of knowledge as old as human warfare: you must lead a moving target.

For a target moving at a constant velocity, or a constant acceleration, or in any other kind of orbit which is mathematically predictable, a computer was not only necessary, but sufficient. In such a case, the accuracy was perfect, the hits one hundred per cent.

But the evasive action taken by a human pilot, aided by a randomity selector, is not logical and therefore cannot be handled by a computer. Like the path of a microscopic particle in Brownian motion, its position can only be predicted statistically; estimating its probable location is the best that can be done. And, in space warfare, probability of that order is simply not good enough.

To compute such an orbit required a special type of human mind, and therefore a special type of human. It required a Guesser.

The way a Guesser's mind operated could only be explained to a Guesser by another Guesser. But, as far as anyone else was concerned, only the objective results were important. A Guesser could "guess" the route of a moving ship, and that was all anyone cared about. And a Master Guesser prided himself on his ability to guess accurately 99.999% of the time. The ancient sport of baseball was merely a test of muscular co-ordination for a Guesser; as soon as a Guesser child learned to control a bat, his batting average shot up to 1.000 and stayed there until he got too old to swing the bat. A Master Guesser could make the same score blindfolded.

Hitting a ship in space at ultralight velocities was something else again. Young Kraybo could play baseball blindfolded, but he wasn't yet capable of making the master guesses that would protect a merchantship like the 

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