one hundred guilty and one innocent -- 8/20/25

20 Aug 2025

one hundred guilty and one innocent -- 8/20/25

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Today's selection -- from Proof by Adam Kucharski. Abraham Lincoln, defending a man accused of murder, used a weather almanac to challenge a key witness’s testimony.

“It was hard to see anything but a guilty verdict coming for William Armstrong. The courtroom listened as the prosecution witness explained how he’d seen Armstrong kill a man one night the previous summer, under the bright light of a full moon. The witness—a man named Charles Allen—had already testified against Armstrong’s alleged accomplice, who’d been convicted of manslaughter as a result.

“Armstrong's defense lawyer was Abraham Lincoln, helping for free as a family friend ahead of his debates with Senator Stephen Douglas. Lincoln sat in the Illinois courtroom with his head thrown back, staring at the ceiling, seemingly bored and oblivious to what was being said. There he remained, expressionless, until his turn came to question Allen. ‘Did you actually see the fight?’ Lincoln asked. ‘Yes,’ replied Allen.

“Lincoln pushed on the details: the time, the distance, the weapon. At 11 p.m., Allen said he had watched from 150 yards as Armstrong swung a weight on a rope, hitting the man's face. Lincoln asked about the moon. Was it really a full moon? ‘Yes,’ said Allen, ‘a full moon, and as high in the heavens as the sun would be at ten o'clock in the morning.’

Title page of the 1739 edition of Benjamin Franklin's Poor Richard's Almanack

“Lincoln then deployed a tactic rarely seen in a courtroom at the time. He turned to the judge and asked for permission to introduce not a witness but a weather almanac. The judge agreed and Lincoln read the crucial entry aloud: on the night of the supposed murder, the almanac recorded that it hadn't been a full moon at all. By 11 p.m., the moon would have been low in the sky and barely visible. In the darkness, and at that distance, there was no way Allen could have identified the murderer.

“Lincoln's unusual ploy was known as a ‘judicial notice.’ Unlike a witness, who may or may not be reliable, the judge had allowed Lincoln to present the almanac as a statement of indisputable fact. The logic that followed was plucked straight from the land of Euclid: Allen said it had been a full moon, but it had not been a full moon, so Allen was lying. The defense rested and by the end of the day the jury had found Armstrong not guilty.

“Those wanting to deliver justice face two main challenges. First, they need to define what is right and what is wrong. We've seen how John Locke's notion that ‘natural rights’ could be the foundation of a legal system, with justice derived from simple logical principles, stumbled in the complexity of the real world. Although the preamble to the US Constitution stated that one of its purposes is to ‘establish justice,’ that did not prevent a civil war and over two dozen amendments. The inevitability of legal gaps and inconsistencies has meant that rules—and their interpretation—must evolve over time.

“Which brings us to the second challenge. Even if a country converges on what its citizens can and can't do, how should they deal with those accused of breaking the rules? Lincoln's almanac tactic dealt in straight facts, but Armstrong's acquittal relied on a hazier concept. The full moon had definitely not happened, but the jury did not have to agree that Armstrong was definitely innocent. They just needed to have at least a reasonable doubt about his guilt.

“The level of evidence needed to convict Armstrong was not the Euclidean ‘certain proof' that Lincoln had contemplated with the Reverend Gulliver on that train from New Haven. Instead, the decision was framed in terms of doubt, probability, and observation. We've seen how, in mathematics and politics, the pursuit of logical perfection gave way to a crisis of contradictions and compromise. In practice, there is more to proof than the purity of axioms, propositions, and demonstrations. We must therefore look at a wider search for truth. A pursuit beyond the comfort of mathematical certainty, where we must confront the inevitability of error.”