1033: Formal Logic

Formal Logic

|< < Prev #1033 (March 23, 2012) Next > >|

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

|< < Prev Random explanation Next > >|

Explanation

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" stipulates that the truth value of both cause and effect (or similarly tied conditions) must be the same. When evaluating one statement based on another, if the condition statement is true, then the conclusion statement must be true, and if the condition statement is false the conclusion must be false. (This is distinct from a simple "if", which leaves the conclusion undefined or unaltered where the condition is false.) In this case, you must honk if you love formal logic, and you are only allowed to honk if you love formal logic (in other words, someone who does not love formal logic is prohibited from honking). The title text elaborates on this, saying, in essence, "Don't honk at me just because you're impatient that I stopped for a pedestrian."

The sticker is somewhat self-referential: 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 Randall altogether, because, understandably, he hates it when he yields for pedestrians only to get honked at by some impatient driver behind him. The ONLY reason the sticker allows you to honk is to declare your love for formal logic. 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.

Transcript

[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

Trivia

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

  Add comment         Create topic (use sparingly)        Refresh 

Discussion

- 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. 108.162.219.58 08:37, 10 February 2014 (UTC)

Why would you even think that is correct? -Pennpenn 108.162.249.205 03:19, 29 January 2015 (UTC)

Elementary, my dear 108.162.219.58! 108.162.254.148 19:50, 8 February 2015 (UTC)

It does not say "honk when you ..." 141.101.104.55 16:54, 19 May 2015 (UTC)

So, what do you do if you hate formal logic? Honk twice? 141.101.104.113 (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)

Can anyone figure out what kind of car this is? RadiantRainwing (talk) 18:28, 31 July 2024 (UTC)

It's the all-new xkcd car! 209.66.205.201 22:04, 12 May 2026 (UTC)
        Add comment