A lot of English idioms come from naval lore — many more than you’d think — but this one still surprised me. — Dan

In English, a “blind eye” is rarely about eyesight. If you turn one, you’re ignoring something obvious — the mess in the kitchen, your kids’ misbehavior, or any other thing that everyone sees but no one wants to deal with. It’s a neat little phrase that suggests quiet, deliberate ignorance — it has nothing to do with actual vision.

But originally, it probably did. And the reason why involves a naval commander who ignored an order during a battle — and won.

In the late 1700s and early 1800s, Europe seemed to be in a near-constant state of war, with France and England repeatedly clashing as each sought to shape the balance of power on the continent. In 1801, Britain was concerned that Denmark was about to ally with France, so the Royal Navy began a blockade of Copenhagen. Hostilities soon broke out, and on April 2 of that year, the standoff turned into a massive naval battle. The fighting quickly became chaotic: Danish ships were heavily fortified, the harbor was tricky to navigate, and British vessels were taking serious damage.

Admiral Sir Hyde Parker commanded the British fleet, but did so from afar. Vice Admiral Horatio Nelson was at the helm of one of the ships, directing much of the battle in real time. Parker, seeing the carnage being inflicted by the Danes, considered the effort lost. As Britannica notes, the Royal Navy used flags as a way to send orders from command to those actually on board the vessels. Per Parker’s instruction — up went the flags signaling that Nelson and the rest of the fleet should disengage.

Nelson believed victory was still within reach and that withdrawing would squander the opportunity. He wanted to ignore Parker’s order — and likely knew his reputation was strong enough that his men would follow him if he did. Nelson was widely regarded as one of the greatest naval commanders in history, thanks to a long string of victories during Britain’s wars against Napoleonic France. His leadership at sea had already become legendary, even during his lifetime. But the signal flags were plainly visible in the distance. How do you ignore an order everyone can see?

That’s where the other part of Nelson’s battle history came into play. Years before his most famous exploits, he had lost useful sight in his right eye after being wounded during a campaign in Corsica in 1794, a mishap that left him permanently half-blind. According to the story widely retold afterward, Nelson used his blind eye to his advantage. As the language site Phrases.org.uk recounts, Nelson lifted his telescope to his sightless eye and looked through it as best he could, which is to say, not at all. He then told those gathered that, “I really do not see the signal,” and, instead, continued pressing the Danish Navy.

Whether the exact words were spoken that way is debated, but the gesture stuck. Nelson continued the attack, the Danish resistance eventually collapsed, and Britain claimed victory. The episode is widely believed to be the source of the phrase “turn a blind eye,” meaning to deliberately ignore something you know is there.

Somewhere along the way, the story of a one-eyed admiral squinting through a telescope became a permanent part of the English language. Today, when someone turns a blind eye, they’re usually just pretending not to notice something inconvenient. Nelson, on the other hand, did it while commanding warships in the middle of a battle — and, inconveniently for his superior officer, winning it.

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Today’s Bonus fact: During World War II, many American submarines used grain alcohol to fuel their torpedo motors. That caused an issue — sailors, far from home and underwater — would siphon off some of that fuel, mix it with juice, and have a little party. (As one torpedoman told the Anchorage Daily News, “the torpedo wasn’t going to use it all anyway, so we kind of tapped off a little bit of it.”) To prevent this, naval authorities began poison the grain alcohol, rendering it undrinkable. One common additive was called “Pink Lady,” a mix of methanol and red food dye. The red food dye served as a warning that the mix contained methanol. And that was reason enough not to drink the stuff. Methanol — which can’t be removed from grain alcohol — causes blindness if consumed in large enough amounts.

From the Archives: Patch Theory: Why pirates wear eye patches (maybe).

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And thanks! — Dan