Direct-Proof Dora

So she presented herself to the judge and declared, "It's always even. I tested three pairs, they all came out even, therefore it holds for every pair." She delivered it briskly, certain, almost impatient — a clean leap straight from a handful of cases to all of them.

The judge was a patient old baker named Mr. Fenn, and he did not simply agree. "Three pairs," he said, turning the number over. "And how many pairs of odd numbers exist in the world, do you suppose?"

"A great many," Dora conceded.

Dora had no intention of asking Cass anything. She was right; she could feel that she was right, and the feeling seemed proof enough of itself. Why should a person be made to crawl through steps toward a destination already in plain view? Surely the obviousness was the argument. She carried that conviction around the fair all afternoon, guarding it the way one guards the pleasant certainty of having won before the results are read.

Cass sought her out regardless, near the ribbon board. "Let me guess your method," he said. "You checked a few instances, they cooperated, and you upgraded 'a few' to 'always.'"

"Because it is always," Dora said.

Dora prepared to explain that her question was different, her certainty more trustworthy, her feeling somehow of a higher grade. But a cold thought had already slipped past her defenses: his certainty had felt exactly as absolute as mine feels now — and his had been a lie. That was the intolerable part. The sensation of being right, it seemed, was issued freely to true and false conclusions alike; it arrived identically either way and named neither. As evidence, it was worthless. It only felt like gold.

She went home that evening thoroughly unsettled and, for the first time, did the thing her certainty had told her to skip. She walked the argument — deliberately, one joint at a time, forbidding herself a single leap.

What is an odd number, precisely? An odd number is an even number with one left over — some collection of pairs, plus a single remainder. So any odd number could be written honestly as a quantity of twos, plus one. Very well: take two such numbers. The first is some twos plus one; the second is some other twos plus one. Add them. All the twos merge into one larger heap of twos — still perfectly divisible into pairs — and then the two solitary remainders, the plus-one and the plus-one, encounter each other and combine into a fresh pair of their own. Nothing is left stranded. She sat very still. The two lonely leftovers had found each other and become even; that was the reason — not "I tried three," not "it feels correct," but a cause that governed every possible pair of odd numbers at once, because at no point had she permitted herself to murmur "and presumably the rest behave." Each step issued directly from the one before it. There was no seam left unattended for a falsehood to hide inside.