"And where does this lead us?" asked Dusty.
"Right back into a circle," said Dr. Ross thoughtfully. "Because if they've developed interstellar travel due to considerations brought about by the mechanus theory, that means that they have proved their theory by practise."
Dusty grunted half-humorously. "Isn't this like saying that mud is sticky because it's gooey? Or that winter is cold because of a lack of heat?"
Ross nodded. "Or that things fall because of the law of gravity."
"But aren't all these things a case of defining 'A' in terms of 'A'?"
"What isn't?" demanded Dr. Ross. "You're not looking for the Universal Truth, are you?"
"No, but—"
"Look, Dusty, the reason that we can afford to accept the fact that one and one adds up to two is simply due to the fact that one and one adds up to two in a great majority of cases."
"Wait a minute, Doc. One and one is always two."
"Not when you add a quart of alcohol to a quart of water. One and one here adds up to about one point eight."