Also called the Politician's Syllogism or Equivocation.
A standard three-step syllogism uses three terms — the things that are being linked by the line of reasoning. If A, then B. If B, then C. Therefore if A, then C. The fallacy of four terms occurs when, exactly like it says, four terms are used instead of three. In most cases, a single term (B) is used two (or more) times, in differing contexts with different meanings; and yet the argument treats the two usages as exactly the same, since the same term was used.
It's best explained by this example from Land of the Blind.
But nothing is better than a big juicy steak.
Therefore, a dry crust of bread is better than a big juicy steak.
This uses two different meanings of the word "nothing." The first line uses "nothing" to mean "a lack of food", while the second line uses "nothing" as "no such thing exists."
This fallacy can often be the core of a joke or pun, such as if someone were to suggest that Batman must be good at baseball, since he's so well-acquainted with bats.
- Hu-Hot Mongolian Grill used this fallacy in a comic radio ad promoting their new "to-go" service, aired in mid 2017. The two people speaking are a museum guard and a woman eating a Hu-Hot To-Go Meal. He tells her that she can't eat that here (in the museum). She replies that certainly she can, it's designed to be eaten anywhere. He repeats that she can't eat it in the museum, adding that there's a "no-food policy". She again asserts that she not only can eat it there, she is eating it there. The term that's doubled-up is "can". The guard is using it in the sense of "allowed or permitted", the woman is using it in the sense of "capable of".
- Anadin pain pills used to be marketed with the slogan "Nothing acts faster than Anadin", prompting the zinger "So take nothing — it's cheaper".
- Garfield expresses the philosophy. "If nobody is perfect, I must be nobody."
- In the Woody Allen film Love and Death, Allen's character Boris gives this monologue: "What would Socrates say? All those Greeks were homosexuals. Boy, they must have had some wild parties. I bet they all took a house together in Crete for the summer. A: Socrates is a man. B: All men are mortal. C: All men are Socrates. That means all men are homosexuals."
- There's an old joke revolving around the word nothing, where a bar patron turns down a beer from the bartender because "nothing is better than a cold drink".
- Related is "There is nothing like a good cup of coffee... and this is nothing like a good cup of coffee."
- Also, "Nothing is better than eternal paradise. A ham sandwich is better than nothing. So a ham sandwich is better than eternal paradise."
- An old joke: When you drink, you get drunk. When you get drunk, you go to sleep. When you go to sleep, you commit no sin. When you commit no sin, you go to Heaven. So, let's all get drunk and go to Heaven!
- Another similar drinking joke: The more I drink, the more my hands shake. The more my hands shake, the more drink I spill. The more drink I spill, the less I drink. Therefore, the more I drink, the less I drink.
- This joke: A kid asks his teacher "You wouldn't punish me for something I didn't do, would you?" The teacher says "Of course I wouldn't." The kid says, "Good, because I didn't do my homework!" (He's changing the meaning of "something I didn't do" from "something wrong that was not done by me" to "something I should have done and failed to.")
- A cat has three tails. No cat has two tails, and one cat has one more tail than no cat; therefore, one cat has three tails.
- Two versions of Fauxtivational Posters in places of education:
Knowledge is power.
- One version:
Study hard. It makes you evil.
Knowledge is power.
Corruption is a crime.
Crime never pays.
Study hard. It makes you broke.
- There is one joke regarding space...and cheese.
Swiss cheese has holes.
Each hole takes the space where cheese would be.
The more cheese you get, the more holes it will have.
As it has more holes, you get less cheese.
The more cheese you have, the less cheese you get.
- In Discworld, libraries warp spacetime because "knowledge=power=energy=matter=mass", and enough mass gives you a blackhole.
- The TheSecretsOfDroon, the Wand of Urik works by making illogical syllogisms true. For example, "Cape is blue/Water is blue/Cape is water" turns a blue cape into a pool of water. Or "Stone is good/Fountain is good/Stone is fountain" turns a demon of stone into an ornate fountain.
- From The Colbert Report:
"I live by syllogisms: God is love. Love is blind. Stevie Wonder is blind. Therefore, Stevie Wonder is God. I don't know what I'd believe in if it wasn't for that."
- An episode of Yes, Minister called this by name, as "The Politician's Syllogism", specifically the form: "Something must be done. This is something. Therefore we must do this." The two different meanings of "something": "A solution to this problem" and "A thing" are mixed and said to be the same.
- Anyone Can Whistle explains in "simple" terms what's wrong with leftists:
The opposite of left is right,
The opposite of right is wrong,
So anyone who's Left is wrong — right?
- Shakespeare did it first. In As You Like It, Touchstone proves that Corin is going to hell because he's never been in court.
Touchstone: Why, if thou never wast at court, thou never sawest good manners; if thou never sawest good manners, then thy manners must be wicked; and wickedness is sin, and sin is damnation. Thou art in a parlous state, shepherd.
- In Twelfth Night, Feste attempts this to make excuse for his lateness:
Olivia: Take the fool away.
Feste: Do you not hear, fellows? Take away the lady.
Olivia: Go to, you're a dry fool; I'll no more of you: besides, you grow dishonest.
Feste: Two faults, madonna, that drink and good counsel will amend: for give the dry fool drink, then is the fool no longer dry; bid the dishonest man mend himself: if he mend, then he is no longer dishonest: if he cannot, let the botcher mend him: anything that's mended is but patched: virtue that transgresses is but patched with sin; and sin that amends is but patched with virtue: if that this simple syllogism will serve, so; if it will not, what remedy? As there is no true cuckold but calamity, so beauty's a flower. The lady bade take away the fool; therefore, I say again, take her away.
- In Hamlet, the gravedigger and Hamlet make wordplay on "lying" (physically remaining in one place and fibbing):
Hamlet: Whose grave's this, sirrah?
Clown: Mine, sir. [sings]
Hamlet: I think it be thine indeed, for thou liest in't.
Clown: You lie out on't sir, and therefore 'tis not yours. For my part, I do not lie in't, yet it is mine.
Hamlet: Thou dost lie in't, to be in't and say it is thine. 'Tis for the dead, not for the quick; therefore thou liest.
Clown: 'Tis a quick lie, sir; 'twill away again from me to you.
Hamlet: What man dost thou dig it for?
Clown: For no man, sir.
Hamlet: What woman, then?
Clown: For none, neither.
Hamlet: Who is to be buried in't?
Clown: One that was a woman, sir; but, rest her soul, she's dead.
Hamlet [to Horatio]: How absolute the knave is! We must speak by the card, or equivocation will undo us.
- Les Luthiers has one example with one of the songs composed by the titular character of the "Manuel Darío" piece. He claims it's philosophical, and that he doesn't get the meaning behind it.
I love you more than my life
My life is you
But if my life is you
And I love you more than my life
Then that means
That I love you more than yourself!
- In this Order of the Stick, the Empress is committing the Four Terms fallacy by using "grown larger" in two different senses: Dragons that are more powerful have grown larger (as a result of age), so she thinks that if she grows larger (by eating more and getting fat) that she will also be more powerful. That's not the only fallacy involved in her reasoning, either; she's also committing False Cause, by attributing power to size.
- Played for laughs in a Histeria! sketch about Rene Descartes (and a number of other jokes on the same topic): After Descartes makes his famous proposition that "I think, therefore I am."Meaning , a cavalcade of distractions cause him to proclaim "I can't think!"meaning , whereupon he disappears in a Puff of Logic.
- The most famous version is probably this:
All the world loves a lover
I love you, therefore I am a lover
You are all the world to me, therefore you love me
- Commonly used in LSAT testing for law school admissions in the United States. For example, using the word interest to mean financial stake, concern, or welfare. "The judge has no financial ties to the settlement with ABC Company. He is completely disinterested." This is not the same thing as saying he is "uninterested."
- Mathematics easily falls prey to this if you ignore a few key rules, e.g.:
x/0 is undefined
0/0 is simultaneously 1,0, and undefined
1 is equal to 0 and both are undefined.
- Also in mathematics:
Women = Time, Money
Since Time = Money,
Women = Money, Money
= Money squared
Since Money = the root of all Evil,
Women = (the square root of Evil) squared
Women = Evil
- Again in mathematics:
Power = Work / Time
Since Knowledge = Power and Time = Money,
It follows that Knowledge = Work / Money
Solving for Money, we get:
Money = Work / Knowledge
As Knowledge approaches zero, Money approaches infinity, regardless of the value of Work.
Therefore: The less you know, the more you make.
- Then there's the story about the parent who buys Hentai for their 10-year-old, only to return it in a rage to the store where they bought it, because in spite of the explicit picture on the front, and the ratings and warnings all over the box, they reasoned that, "It's animated, cartoons are animated, and cartoons are for kids, so it must be for kids!"
- A less humorous one is parents or other authority figures mixing the meanings of "respect" in the form of "If you don't respect me [obey my authority] I won't respect you [treat you like a real person]."