Words can carry an argument somewhere it never earned.
The idea
An argument can go wrong when a word changes meaning halfway through. Here's a joke. Nothing is better than a good holiday, and a cold sandwich is better than nothing. So a cold sandwich beats a good holiday? No: 'nothing' meant two different things. This slip is called equivocation.
Here's another. A feather is light. Whatever is light can't be dark. So a feather can't be dark. The first 'light' means not heavy; the second means not dark. Each step sounds fine on its own, which is why the slip is easy to miss. Spotting it means asking what each 'light' means.
A second trick changes a definition to dodge an awkward example. Someone says no real fan leaves a match early. Told about a lifelong supporter who left early once, they reply: 'Then he isn't a real fan.' The claim only survives because the meaning of 'real fan' quietly changed. The trick is nicknamed 'no true Scotsman', after a story a philosopher once told. The name sums up the dodge: no true member of the group would do that.
A word with two meanings isn't a problem in itself. In logic, 'begging the question' means an argument that assumes the very thing it sets out to show. In everyday talk it's also used to mean 'that raises the question', and one major dictionary lists both. Using the phrase in either sense is fine. With any two-meaning word, trouble starts when an argument switches senses partway.
Want the research, names and dates? They are in Go deeper, at the end.
Exact-looking numbers that can't be compared.
Picture it
Picture a tape measure that stretches a little between readings. Each reading looks exact. But two readings taken with it can't be compared. Nobody misread a single number; the tape moved. A good tape stays the same length all day. A shifting word does to an argument what a stretching tape measure does to measurements.
For a child: At break time, the rule is 'whoever is fastest wins.' You win the race. Then the other kid says, 'Fastest means fastest at climbing.' The rule changed after you won. You didn't get any slower. The word 'fastest' just moved. Nobody would call that a fair race.
Where an argument's weight can rest.
How it applies
Most of the work is in noticing one word. Many arguments lean on one word that does a lot of work, like 'real', 'natural' or 'fair'. Its meaning at the start can be set beside its meaning at the end. If they match, the argument can be judged on its reasons. If they don't, the conclusion hasn't been earned yet. Words that carry praise or blame, like 'fair' or 'natural', are common places for it. A definition given up front is just someone being clear. A definition that appears only after an awkward example is worth a second look. Slips like these can happen by accident, too.
At work, online and at home.
Where you’ll see it
- At work: "The project is finished" meant the writing was done, then becomes "so it can launch", as if tested.
- Online: a post says something is now "legal", then argues as if "legal" meant "a good idea".
- At home: "We agreed to share the chores" meant half each to one person and whoever has time to the other.
Signs it’s happening
- A key word means one thing at the start and something else by the end, and nobody says so.
- A group gets redefined right after someone names an awkward example.
- The conclusion feels like a magic trick, and you can't see where the meaning slipped.
Same pizza, two meanings of fair.
Before and after
Two friends split a pizza. Earlier one said 'fair means equal'. Now they say, 'It's only fair I get more, I'm hungrier.'
"That's fair, you said so." The word 'fair' got a pass, though it now means something else.
"Which fair do you mean: equal shares, or by need?" Pinning the word down first shows what the claim says. Then each version can be weighed.
One question about Rome, more than one fair answer.
A story from history: When did Rome fall?
- Ask when Rome fell, and the usual answer is 476. That year a boy emperor in Italy, Romulus Augustulus, was removed. Yet the city of Rome itself had already been captured and looted twice, in 410 and 455.
- But the Roman Empire had two halves, and only the western one lost its emperor that year.
- In the east, Roman emperors went on ruling from Constantinople until 1453, nearly a thousand years more.
- Even in the west, 476 isn't the only date you could pick. The emperor before the boy, Julius Nepos, had been driven out by the boy's father. Nepos went on claiming the title until he died in 480. He even had coins issued in his name in Italy. One historian notes 476 was picked as the date in Constantinople, in the sixth century, for political reasons.
- Historians also argue over the word "fall". The western empire's losses came over about a century, not in one blow. Some see real decline in the west. Others, more interested in religion and culture, speak of new things rising rather than an empire falling.
When Rome fell depends on which Rome you mean, and what counts as a fall. Once the words are pinned down, each answer can be checked. The western date, the eastern date and the argument over decline answer different questions.
Quick check3 questions · nothing is saved
1. What goes wrong in the cold sandwich joke?
2. Someone says a lifelong fan 'isn't a real fan' after hearing he left early. What are they doing?
3. Why is 'When did Rome fall?' hard to answer with one date?
One question worth keeping.
In one line
An argument is only as steady as the words it leans on.
Which word have you heard stretched to win an argument, and what did it mean at the start?
Go deeperThe research, names and dates
Where this comes from
The Internet Encyclopedia of Philosophy defines equivocation as "the illegitimate switching of the meaning of a term that occurs twice during the reasoning". The word is used twice, in two senses, so the conclusion only seems to follow.
The Stanford Encyclopedia of Philosophy says the history of the study of fallacies begins with Aristotle's On Sophistical Refutations. That short work describes thirteen ways an argument can look like a refutation, or disproof, without being one. Aristotle split them into those that depend on language and those that do not. In W. A. Pickard-Cambridge's translation, one is "ambiguity".
"No true Scotsman" protects a generalisation from a counterexample by redefining the group: no true member would do that. The Internet Encyclopedia of Philosophy calls it a kind of ad hoc rescue of a generalisation. That means a fix added just to save it, with no other reason behind it. The name comes from a story told by the philosopher Antony Flew.
Begging the question, in Latin petitio principii, is a form of circular reasoning. The conclusion is derived from premises that presuppose it. In everyday English the phrase is also used to mean "that raises the question", and Merriam-Webster lists both senses.
A shifting word vs a shifting definition
| Compared | Equivocation | No true Scotsman |
|---|---|---|
| What changes | The meaning of a word used twice | Who counts as a member of the group |
| What it does | Makes a conclusion seem to follow | Keeps a generalisation safe from a counterexample |
| Example | "Light" as not heavy, then as not dark | "Real gardener" redefined to leave out a prize-winning one |
Both definitions follow the Internet Encyclopedia of Philosophy. It calls the second a kind of ad hoc rescue. That means a fix added just to save it, with no other reason behind it.
More examples
Everyday words that can mean two things. Some to watch for.
- If a friend says 'I'll be there soon', the word to watch is 'soon': their soon and yours may differ.
- If a sign says 'Fresh bread', the word to watch is 'fresh': baked this morning, or just not stale?
- If someone says 'Nobody reads anymore', the word to watch is 'reads': books only, or news and messages too?
What if…?
- What if I spot a slipped word: does that mean they're wrong?
- Not by itself. Calling an argument flawed "says nothing about the truth or falsity of the conclusion", as one guide to fallacies puts it. A weak argument can still reach a true conclusion.
- What if they were only making their meaning clear?
- That happens, and it's fair. A meaning given before any example is ordinary care with words. What usually gives a dodge away is timing: the meaning shifts just after an awkward example turns up.
- What if every word has some give in it?
- It usually does. In a paper, three researchers argued that "almost every known type of fallacy is a close neighbor to sound inferences or acceptable moves in a debate". A shift matters when the conclusion rests on it.
Words you may meet
- equivocation
- A mistake in reasoning where a word used twice in an argument quietly switches meaning, so the conclusion only seems to follow. Glossary →
- no true Scotsman
- Protecting a general claim from a counterexample by redefining the group, as in 'no true member would do that'. Glossary →
- begging the question
- In logic, an argument that assumes the very thing it is trying to prove, so its conclusion is hidden in its starting point. Glossary →