“Sir, I acknowledge that there are numerous anomalous differences. However, those differences fall in areas where the definition of a human has a wide latitude, such as skin color and covering, dimensions, and vocal timbre. The similarities are in more fundamental areas such as bilateral symmetry, bipedal locomotion, oxygen respiration-”

“They are humanoid, as you are. But they are not human.”

“I note your assertion, sir, but I am unable to confirm it.”

Derec understood that he was not being called a liar. When it had no independent knowledge, a robot would ordinarily accept the word of a human as gospel. But a robot was under no obligation to accept a human’s claim that it was raining when its own sensors told it otherwise.

This was not that clear-cut an issue, but the robot was biased toward a generous definition of what a human was. Otherwise there was the danger of a robot’s being used as an assassin by the simple step of persuading it that its target was not a human. Derec understood, but even so was annoyed. “I suppose that if they had twelve arms and belched fire when they talked, you might believe me.”

“Sir, in the matter at hand the morphological considerations are not primary in my analysis.”

“Explain. What are the discriminators?”

“Sir, I base my conclusion on the observation that the organisms called Aranimas and Wolruf are intelligent beings capable of independent reasoned thought.”

“How do you know?”

“Sir, you carried on a dialogue with each of them. Although humans on occasion talk to nonanimate objects and may give the appearance of carrying on a dialogue with certain animals, I perceived your discussions as having a qualitatively different character.”

“Are you saying that because I treated them as human, you have to think of them that way?”

“Where there is uncertainty, as thee may be when a human wears a costume or disguise, I am obliged to use such cues as are available. Your behavior created a strong presumption that Aranimas and Wolruf are human.”

“I talk to you the same way I talked to them. Does that make you a human?”

“No, Derec. I am a robot, a technological artifact. To the degree that I may seem to be human, it is only because I have been designed to do so in order to more easily interact with humans.”

Derec was growing frustrated. “Tell me this, then. How do you tell the difference between a robot and a human at a distance?”

“Sir, just as I have an operational definition of that class of organisms called humans, I also have one of that class of objects called robots. It is ordinarily possible to distinguish between the two based on the characteristics they do not have in common. It is not a perfect system, however, and may be fooled, as by a humaniform robot of the type developed by Dr. Han Fastolfe.”

Derec had to concede the point to the robot.If only I could show it skin scrapings from the three of us-but if Aranimas or Wolruf happened to have a cellular structure, I’d be no better off. It might even decide its right arm is human-

“Robot, are Spacers, Settlers, and Earthpeople all human?” he asked suddenly.

“Yes.”

“Have you personally observed every member of those groups?”

“No, Derec. There are approximately eight billion Earthpeople, five billion Spacers, and-”

“If you have not observed them individually, how is it you are able to classify them all as human?”

“Spacers and Settlers are descendants of the original human community on Earth,” the robot replied. “Therefore, any individual correctly identified as a Settler or Spacer cannot be other than human.”

“Why is that?” Derec asked, though he knew the answer.

“They share a phylogenetic relationship. The offspring of a human must be human.”

“In other words, what really counts is biology-the genes and DNA humans carry in their cells.”

“Yes.”

“And the guidelines that are built into your definition of a human are simply shortcuts to make it unnecessary for you to subject everyone you encounter to a biological assay. The final criterion is DNA.”

“That is correct, Derec.”

“But you have no way of examining a person’s DNA directly.”

“No, sir.”

“Fine. You said that each of the anomalies in Aranimas’s appearance fell within the acceptable parameters for natural variation and mutation.”

“Yes, sir.”

“I ask you to calculate the probability that all of Aranimas’s anomalies would appear in a single organism.”

The robot scarcely hesitated. “The probability is extremely small.”

“And for Wolruf?”

“The probability is somewhat higher, but still on the order of one chance in ten to the fifteenth power.”

“In other words, there is less than a one in ten thousand chance that a mutation this extreme would have arisen once in all of human history. And here there are two of them, not only alive at the same time but in the same place, and both as different from each other as they are from me.”

“It is quite remarkable. No doubt further study of these individuals would be of great benefit.”

Derec sighed exasperatedly. “Listen, my thick-headed robot friend. Stop thinking one step at a time. Isn’t the probability that an independently evolved lifeform might be bipedal, bilateral, and oxygen-breathing greater than the probability that these creatures are mutant humans? Can’t Aranimas and Wolruf be intelligent without being human?”

“Yes, that is possible.” The robot paused, a sign of great activity in its positronic pathways. “However, since no independently evolved intelligent lifeforms are known, it is difficult to assign a probability to a specific form.”

“I challenge your premise,” Derec pounced. “Why are most robots humanoid?”

“Higher robots are humanoid because it is a successful generalized design and because-”

“The other reasons don’t matter,” Derec said. “Apply that standard to the question of Aranimas and Wolruf.”

Again the robot paused before answering. “My positromotive potentials are extremely high on both sides of the question,” it said at last. “I believe this state may be similar to that which a human describes as confusion.”

“Get to the point. What’s the verdict?”

“It is my tentative conclusion that Aranimas and Wolruf are not human.”

“You are not obliged by the First Law to protect them or the Second Law to obey them?”

“No, Derec.”

“Good,” he said with relief. “You can live. Now listen closely. I have some important instructions for you concerning our alien hosts-”

Chapter 11. Tampering

Within the greater world of the raider ship, Derec had been confined to one small island. As he prepared to begin his nocturnal wanderings, that island consisted of the route from the lab (in what he thought of as Hull L) to the dispensary and Personal (in Hull D). Linking the ends of the trail were two sections of storage corridor forming a short transfer tunnel between the hulls. And that was all Derec knew.

He did not know where the lab was in relation to Aranimas’s command center, though he felt certain that it was some distance away. For that matter, he did not know the way to any of the other places he had been-the hull where he had seen the star-creatures, the corridor in which he had awoken, the hold from which the salvage team had operated, the section of lockers where the robot parts had been stored. He did not know where Wolruf slept, or where the fifty Narwe were most likely to be found.

The corridor to the dispensary was also the only part of the ship which he had explicit permission to be in. Aranimas had not forbidden him to roam farther afield, but neither had he invited it. It seemed to Derec as though it might be some kind of test. The problem was, he didn’t know whether he would fail through action or inaction: by exploring, or by staying close to home.