Please enter your PIN number

The cash machine asks you to enter your PIN number, and you do, without a flicker of protest. But the N in PIN already stands for number — personal identification number — so the machine has just asked for your personal identification number number. It is, of course, an ATM machine, which is to say an automated teller machine machine. You will confirm the details on its LCD display — its liquid-crystal display display — and if it goes wrong you will worry about catching a computer virus, or an HIV virus, which is a human immunodeficiency virus virus.

Once you start noticing, you cannot stop. We say the same thing twice constantly, in perfect good faith, and almost never hear ourselves do it. There is even a name for the acronym version of the habit, coined in a light-hearted New Scientist column in 2001: RAS syndrome. It stands for "redundant acronym syndrome syndrome" — a joke that diagnoses itself.

Please RSVP, at 3 a.m. in the morning

Acronyms are where the redundancy is easiest to spot, because you can unfold them. "Please RSVP" politely begs you to please répondez s'il vous plaît — please respond if you please. We speak of the ISBN number on a book, the SALT talks between Cold War powers (strategic arms limitation talks talks), the CNN network, a UPC code, an ABS braking system. Each one takes a set of initials, quietly forgets what the last letter was doing there, and hires a fresh English word to do the same job.

The pattern is not limited to abbreviations. It is all over ordinary time and measurement, too — the 3 a.m. in the morning, the frozen ice, the free gift, the added bonus, the close proximity. But those are just sloppy doublings we could tidy up if we tried. The interesting ones — the ones that reveal something about language itself — are the redundancies we could not fix even if we wanted to, because the repeated word is hidden inside another language.

The the tar tar pits

Los Angeles has a famous fossil site called the La Brea Tar Pits. In Spanish, la brea means "the tar." So the full name, unfolded, is the the tar tar pits — the definite article doubled, the word for tar doubled, all in one tidy tourist sign. It is probably the most-loved example of a tautological place name: a name that says its own meaning twice because two languages each took a turn labelling the same thing.

Look at a world map with this in mind and the doublings are everywhere. Cross a border and a word turns to scenery; the next people along, not hearing the meaning in it, add their own:

• The Sahara Desert — from Arabic ṣaḥrāʾ, "desert." The Desert Desert.
• The River Avon (there are several in England) — from a Celtic word afon, "river." The River River.
• Lake Tahoe — from the Washo dá'aw, "the lake." Lake Lake.
• The Mississippi River — from Ojibwe misi-ziibi, "big river." The Great River River.
• The Sierra Nevada Mountains — Spanish for "snowy mountain range." The Snowy Range Mountains.

Even the sky is not safe. Our galaxy is the Milky Way — but galaxy comes from the Greek galaxías, "milky." Say "the Milky Way Galaxy" and you have said milky twice, once in English and once in ancient Greek, about the same faint band of light. The word crossed two thousand years and one language, and lost its meaning in transit.

A tautological name is a fossil. It marks the exact spot where a word stopped meaning anything to the people using it.

Chai tea and the hoi polloi

The same thing sits on your plate and in your cup. A café will sell you a chai tea latte — but chai is simply the word for "tea" across a huge sweep of Asia and eastern Europe, so "chai tea" is tea tea. (It is a distant cousin of the very word tea: both descend from Chinese, one by the land route and one by sea, a split we've written about in two words for tea.) Order naan bread and you have asked for bread bread, since nān already means bread. A menu of soup du jour of the day and queso cheese writes the redundancy out in full.

Speech does it too, and here even careful writers get caught. To sneer at "the hoi polloi" is to sneer at the the many, because hoi is already "the" in Greek. To salsa dance is to sauce dance. To wear a corduroy fabric, drink a panini sandwich (the plural of an already-plural word), or admire the artwork on a manga comic is to double up across a border every time.

What redundancy is really telling us

That is the thread running through every example, from the ATM machine to the Desert Desert. A word arrives from somewhere else. At first it carries its meaning openly. Then, borrowed into a new language and cut off from its family, it goes opaque — it becomes a label with nothing legible inside it. And a label with no visible meaning feels incomplete, so we quietly bolt a native word onto it as a signpost: tar after brea, number after PIN, tea after chai. The redundancy is not a mistake. It is the sound a word makes when it has become pure surface.

Which is worth pausing on, because it describes something that happens inside every language learner. A word you have only ever met as a flashcard pair — a foreign shape on one side, an English gloss on the other — is exactly this kind of opaque token. It is a brea to you: a sound with a translation stapled on, and no meaning you can feel from the inside. That is why such words slip away so fast, and why, when you reach for them, you so often have to reach for the crutch of the translation first.

A word you truly know is the opposite. It is transparent. You do not translate tea in your head, and you do not need anyone to add "the drink" after it, because the meaning is simply there, fused to the sound. The whole project of learning a language is turning opaque tokens into transparent ones — carrying words far enough across the border that they stop being scenery and start meaning something again.

How a word becomes transparent

You cannot will a word transparent by staring at its translation harder. Transparency is built the same way it was built for every word you already own: by meeting the word in real sentences, in situations that give it a meaning of its own; by learning its reasons and its relatives rather than a bare gloss, so it is hung on something you already understand; and by meeting it again and again, spaced across days, until you no longer have to fetch the translation because the meaning arrives on its own. The tautologies of the world are simply what happens when that last step never comes — when a word is handed on but never truly learned.

This is the whole idea behind vocabla: words met in context, with their meanings and their families around them, a handful at a time, and brought back until they come without being called. Do that, and your new words stop being labels you have to prop up and become words you simply mean. You will still order a chai tea, of course — the redundancies are far too charming to give up. You will just be one of the few people in the queue who can hear the joke.