"Okay. Now. A man travels in time," he said. "He travels in time and fifty million years ago he steps on a moth. _Fantastic._ You wouldn't believe the effect one humble moth could have! The man returns to the present and finds to his guilty astonishment that the Empire State building is now flying the Bolivian flag and gargoyles are sticking out of the 79th floor. This is cute so be careful of it. Boy meets moth, boy loses moth--gargoyles! Except that all those not completely devoid of common sense or debauched by poetic license would know that if the gargoyles were there they were there before he went back in time. His own body is a part of a continuum of which those gargoyles are a prior sequential segment; his entire life is so inextricably wrapped up in those gargoyles that he couldn't possibly be surprised by them, or by any other change he'd caused. As he returned to the present his memory would _alter_. To take any other view of this--to close your eyes and hide behind paradox--is going to get us all in trouble because you've got yourselves a real time traveler now and it's about time you started _thinking_ about these things." ("Well why didn't you say so," Blackburn murmured. "Be glad to think about it, give it _every_ consideration. We'll be in touch." "I don't think he heard you," Shaheen said.) "I won't even bother discussing the suicide-by-killing-old-grandpa myth," Pendelton buzzed on with a great deal of imperturbability, "other than to point out there is no such thing as negative feedback as applied to human beings. I realize that's only a small nuance. But then, take care of the nuances and the breakthroughs will take care of themselves, I always say." ("Oh Lord," Blackburn whispered.) * * * * * "Another small point. I hate to verbalize the obvious like this but it clears the ground, don't you think? I realize you two might like to traipse back through time and have a friendly chat with, say, Mike Faraday. But that's exactly what you can't do. You know a _little_ too much about time machines. He'd pick your brains in half an afternoon and beat you back to your own office. As I say that's only a nuance. It's a nuance that eliminates 75% of all time travel science fiction ever written but that's still only a nuance, wait till I get to the Great Implication."