The Positronic Man by Isaac Asimov, Robert Silverberg

I mean. Friends are friends and machines are machines and they should not be confused. One may love another person but one ordinarily does not love a household appliance, however useful or attractive or pleasing it may be. All Andrew is is an ambulatory computer, Mr. Martin, a computer that is endowed with artificial intelligence and has been placed in a humanoid body-frame and so gives the superficial appearance of being something quite different from the computers that guide our air traffic and operate our communications systems and do all our other routine chores. The personality that your daughter believes she perceives in Andrew, and which you say has caused her to 'love' him, is merely a simulated personality, a pre-designed construct, wholly synthetic. I beg of you, Mr. Martin: never forget that a computer with arms and legs and a positronic brain is still nothing but a computer, albeit a somewhat enhanced computer. A machine. A gadget, Mr. Martin. A household appliance."
    "I will keep that in mind," said Sir in a dry, cool tone. "You know, Dr. Mansky, I've always endeavored to think clearly and in an orderly way. I never confuse an arm with a leg or a hand with a foot or a cow with a horse, and I'll do my best not to confuse a robot with a human being, however great the temptation may become. Thank you very much for your advice. And now, if you'd like to have a quick tour of Andrew's workshop-"

Five
    MISS HAD BEGUN to cross the threshold that truly separates girlhood from womanhood, now. She was enjoying an active social life and going off with her new friends-not all of them girls-on excursions to the mountains, to the deserts of the south, to the wilderness to the north. Her presence in the Martin house was becoming an increasingly rare event.
    So it was Little Miss-not as little as before-who filled Andrew's horizon now. She was turning into a coltish, tireless girl who loved to run great distances along the beach, with Andrew effortlessly keeping pace beside her. She went rambling in the forested areas adjacent to the house, and relied on Andrew to help her down when she had scrambled a little too far up some tree to peer into a bird's nest, or when she had trapped herself on some precarious rocky ledge that she had climbed for the sake of getting a better view of the sea.
    As ever, Andrew was vigilant and endlessly protective as Little Miss romped about. He would let her take her little tomboyish risks, yes, because they seemed to make her happy, but not without his calculating the real risk of anything serious happening to her, and he was always poised and ready to intervene swiftly on her behalf if that should be necessary.
    The First Law, of course, compelled Andrew to exert constant diligence to protect Little Miss from harm. But, as he sometimes told himself, he would willingly and gladly defend her against peril of any sort even if the First Law did not exist.
    That was an odd thought: that there might be no First Law. Andrew could barely conceive of that The First Law (and the Second, and the Third) were such fundamental aspects of his neural pathways that it made him dizzy to imagine himself without them. And yet he had imagined it. Andrew was puzzled by that: how strange, having a capacity to imagine the unimaginable! It made him feel almost human, when paradoxical concepts like that went through his mind.
    But what did almost human mean? That was another paradox, and an even more dizzying one. Either you were human or you were not How could there be any sort of intermediate state?
    You are a robot, Andrew reminded himself sternly.
    You are a product of the United States Robots and Mechanical Men Corporation.
    And then Andrew would look at Little Miss and a sensation of great joy and warmth would spread through his positronic brain-a sensation that he had come to identify as "love"-and he would have to remind himself, allover again, that he was nothing more than a cleverly designed structure of metal and