1033: Formal Logic

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Formal Logic
Note that this implies you should NOT honk solely because I stopped for a pedestrian and you're behind me.
Title text: Note that this implies you should NOT honk solely because I stopped for a pedestrian and you're behind me.


This comic is a riff on bumper stickers that say "honk if you love ____". Here, the subject is formal logic, but the word "if" is replaced with a formal logic term "iff," which means "if and only if".

The term "If and only if" sets two separate requirements, both of which must be met. In this case, you must love formal logic in order to be allowed to honk, and you must honk if you love formal logic. (Conversely, someone who does not love formal logic is prohibited from honking, and someone who loves formal logic cannot refuse to honk.) The title text further elaborates on this, saying in essence: "Don't honk at me just because you're impatient that I stopped for a pedestrian."

The joke is the contained self-reference: you have to love formal logic to take the sticker seriously and honk for exclusively that reason. The title text reveals the sticker is actually there to stop people from honking at him altogether, because Randall understandably hates it when he yields for pedestrians only to get honked at by some impatient driver behind him; the ONLY reason you're allowed to honk is to declare your love for formal logic. So by extension, if someone DOES honk while he is stopped for a pedestrian, he can simply enjoy the idea that the other driver loves formal logic rather than being impatient, transforming what might otherwise be an irritant into pleasure.


[The rear end of a car (with an unreadable license plate), with a bumper sticker above the tailpipe to the right:]
Honk iff you love
formal logic


This comic used to be available as a sticker in the xkcd store before it was shut down.

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- What can we learn from this? - I've learned that everyone who drives a car loves Formal Logic that if they press a horn actuator while driving, a horn will sound (Thank you Mr. XKCD). Now can I comment if I love your undeniable genius and your unexpected life's lessons? - E-inspired (talk) 14:36, 28 February 2013 (UTC)

"So, there is nothing you can do except starting to love formal logic" That isn't what this comic means. It means "I am a fan of formal logic, and if you are too, you may honk to indicate this. If you honk for any other reason at all, don't be surprised if I jam a pitchfork up your ass." Re-write, please. 08:37, 10 February 2014 (UTC)

Why would you even think that is correct? -Pennpenn 03:19, 29 January 2015 (UTC)
Elementary, my dear! 19:50, 8 February 2015 (UTC)
It does not say "honk when you ..." 16:54, 19 May 2015 (UTC)

So, what do you do if you hate formal logic? Honk twice? (talk) (please sign your comments with ~~~~)

The "iff" statement also means "if you don't love formal logic, you're not allowed to honk at all". Zowayix (talk) 04:23, 20 August 2020 (UTC)