Explain xkcd: It's 'cause you're dumb.
The comic is a play on the classic wolf, goat and cabbage puzzle belonging to the river crossing puzzles, and first known from Propositiones ad Acuendos Juvenes, with the same setting as here. The three possessions change between various retellings but it typically involves a carnivorous animal (wolf, lion etc.), a herbivore (goat, sheep, chicken, goose etc.), and some plant based food (cabbage, grain, beans etc.). The objective is to ferry all three possessions to the other side of a river safely in a small boat, with the limitation of only being able to transport one possession per crossing. The crossing order must take into account that the carnivore would eat the herbivore if left alone together, and the herbivore would eat the food.
The traditional solution would be:
| Cueball, Wolf, Goat, Cabbage
| Trip 1: Take goat across
| Wolf, Cabbage
|| Cueball, Goat
| Trip 2: Return alone
| Cueball, Wolf, Cabbage
| Trip 3: Take cabbage across
|| Cueball, Goat, Cabbage
| Trip 4: Return with goat
| Cueball, Wolf, Goat
| Trip 5: Take wolf across
|| Cueball, Wolf, Cabbage
| Trip 6: Return alone
| Cueball, Goat
|| Wolf, Cabbage
| Trip 7: Take goat across
|| Cueball, Wolf, Goat, Cabbage
(Note that, since the conditions for this problem are symmetric, an alternate solution would be to transport the wolf on Trip 3 and the cabbage on Trip 5.)
By leaving the wolf behind, four steps are saved — the comic's "step 4" is just a comment — and the troublesome wolf, a wild and dangerous animal not usually kept by humans, is eliminated from the picture.
This could be seen a jab on the common assumption that logic puzzles only have one correct solution. Thus one often keeps the other person thinking and guessing until they arrive at the pre-defined solution, no matter how many other creative good solutions they come up with. Also note that the "problem" given doesn't even state an objective, just three prerequisites.
The title text says that cabbages are also unnecessary, but goats are fine. The reasons for these opinions are less obvious than the one about the wolf, but still understandable. Many people, presumably including the narrator, do not like the taste of cabbage. Many are also fond of goats, finding them cute. The same opinion about goats is in 1282: Monty Hall.
- [A person shows up at a boat docked at the edge of a river. The person has brought along a head of cabbage, a goat, and a wolf.]
- Problem: The boat only holds two, but you can't leave the goat with the cabbage or the wolf with the goat.
- [The wolf looks curiously at the cabbage that's been left behind while the person goes off with the goat.]
- Solution: 1. Take the goat across.
- [The goat remains tied up on the far side. The wolf watches the person come back.]
- 2. Return alone.
- [The wolf sits and waits as the person goes off.]
- 3. Take the cabbage across.
- 4. Leave the wolf. Why did you have a wolf?
- [The wolf goes off.]
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Why not take the boat as well? The goat could drag it around, and you could use it as a makeshift shelter until you finish building a proper house. Also, why does cabbage weigh as much as a goat? Davidy22(talk) 05:50, 14 November 2012 (UTC)
I'd say that the wolf is the only one amongst them he should keep. Seeing as how the wolf doesn't treat Cueball like the goat--i.e. rip him to shreds--and actually fears him enough to even respect the goat in his presence, I'd say that the wolf is well broken-in and might make a good companion. The goat, on the other hand, is just dead weight. (Sure, Cueball could eat her, but that's why he has the cabbage.)
 Take the cabbage across  Return alone  Find the goat problem solved--and your friend well-fed  Take the wolf across 184.108.40.206 06:33, 14 November 2012 (UTC)
- I am not the only one, then! I like wolves a lot more than goats. Then again, I simply like wolves. Greyson (talk) 03:48, 15 November 2012 (UTC)
- They're like puppies! Except instead of love them, you have to occasionally beat the shit out of them to ensure that they continue to fear and respect you. Oh, and instead of love you back, they sometimes physically challenge your authority over the "pack". But yeah, they're all around awesome. 220.127.116.11 09:42, 15 November 2012 (UTC)
- I compare such a relationship (especially the "beat up the wolf in order for the wolf to fear you") to Untoward's relationship with a pig. Greyson (talk) 15:03, 19 November 2012 (UTC)
- Wolves are awesome in Minecraft just as in real life. And all you need is bones and rotting meat. 18.104.22.168 23:01, 10 March 2014 (UTC)
- You're never alone with a goat - ask Alexander Selkirk. 22.214.171.124 13:03, 25 October 2013 (UTC)
Why would cabbage count towards the total capacity of the boat? Take the wolf and the cabbage, return alone, take the goat.--126.96.36.199 08:08, 14 November 2012 (UTC)
- Maybe it's a sentient boat that knows how many passengers/objects are aboard no matter their weight?--Dangerkeith3000 (talk) 16:09, 14 November 2012 (UTC)
The comments describing other shortcuts are really just emphasizing the joke in this comic. The logic puzzle introduces arbitrary constraints and asks the solver to come up with a solution. (This is reminiscent of the classic xkcd on Nerd Sniping.) Most normal people would have the responses you listed about the constraints being arbitrary, but the people vulnerable to Nerd Sniping (i.e. nerds) usually are willing to ignore reality to solve a puzzle with artificial constraints. The purpose of the puzzle is to encourage logical thinking. (Maybe I should take the wolf first so it can't eat the goat. Oh, but then the goat would eat the cabbage. But if I take the cabbage first, the wolf would eat the goat. Therefore, I must take the goat first. ... Continue reasoning with trial and error until the puzzle is solved...) However, you correctly are pointing out how artificial the constraints on the puzzle are. In the actual comic, the solution of leaving the wolf behind would come as a humorous surprise to the nerd following along coming up with a solution. S (talk) 00:07, 15 November 2012 (UTC)
- And that would be the long way towards the 'Explanation' section 188.8.131.52 09:42, 15 November 2012 (UTC)
- I don't think you attitude is as common as you're claiming it is, nor that it is the central joke of the comic, which is probably just about the unlikeliness of the scenario. Here's[] a clip of a comedy episode where 'normal people' are trying to solve the problem straight and a nerd is missing the point.184.108.40.206 13:11, 23 July 2017 (UTC)
I see this as a play on the common use of “logical” to mean “consistent implicit goals or values,” as oppose to “consistent with the principles of inference” as in formal logic. For example, it's the former usage we see when Spock in Star Trek II says, “Logic clearly dictates that the needs of the many outweigh the needs of the few,” or in Star Trek IV, he says, “To hunt a species to extinction is not logical.” You leave the wolf because it’s not logical to hang around wolves longer than necessary –they’re dangerous. Of course, this usage of “logic” is highly relative and subjective (in contrast to formal logic). As some have argued, wolves are not only logical, but awesome. Title text drills home how subjective and relative this use of “logic” is. It’s not logical to take the cabbage because I don’t like cabbage. But I like goats so they “make sense.” --Emzed (talk) 18:40, 30 November 2012 (UTC)
Everybody knows the classic wolf, sheep and cabbage problem, but I just realized that this is not same problem! Just read the first panel: you have the constraints that the boat can carry two and you can't leave the goat with the cabbage or the wolf with the goat as in the classic problem, but nowhere is stated that you must reach the other side with the other three! You can just do nothing, or carry the sheep on the other side and go away with the boat...
--Sandman (talk) 20:02, 16 November 2012 (UTC)
- The problem actually doesn't state any requirement. An equally valid solution would be you starve to death, the cabbage rots to slime and the goat runs away while the wolf tears strips of flesh from your corpse. 220.127.116.11 23:23, 5 December 2012 (UTC)
- Alternate Solution: Share the Cabbage with the goat. The wolf obviously respects you, so take it with you to make your pet. Don't let the goat ride- make it swim. -- 18.104.22.168 (talk) (please sign your comments with ~~~~)
- When I was a kid, we used the version with a dog, a chicken, and a bushel of corn. Being a farm kid, my solution was: take chicken, shoot dog, take corn. Because why the hell do you have a dog that eats chickens? Also, tie your bag o'corn up properly so a chicken couldn't get in. They're not that smart. And they cannot eat a bushel of corn in the time it takes you to cross a river and come back. Also, how did you manage to get to this point without everybody eating each other? Why isn't the chicken in a cage? That could protect it from getting eaten. Is it just sitting quietly awaiting your command? Won't it just wander away once you get it to the other side?
To the above: Goats HATE water. They do not swim well either. I think the wolf should swim.
My solution to the wolf/goat/cabbage is to tether the goat and the wolf far away from each other, whichever side they may be on. --22.214.171.124 22:29, 17 February 2013 (UTC)
Goats eat cabbage..
126.96.36.199 09:18, 13 January 2013 (UTC)
- Hmm... what is to keep the human from eating the cabbage?
- Send the wolf with the cabbage across and let the boat drift back, and then have the human go across with the goat. 3 steps. The real challenge of this puzzle is teaching your wolf to paddle the boat across. Zyxuvius (talk) 09:55, 25 October 2013 (UTC)
Fastest solution: Get the goat in the boat, drop the cabbage in the water, row boat across, periodically pushing the cabbage in the direction of the shore with your oars. 1 step. 188.8.131.52 04:52, 10 January 2014 (UTC)
The river isn't that wide. Couldn't you just throw the cabbage across, then return and get the wolf, then return and get the goat? Or just leave the cabbage. Jake (talk) 14:37, 20 January 2014 (UTC)
Why wouldn't the wolf eat the cabbage? And why would the cabbage's presence stop the wolf from eating the goat (or does it not stop it)? Z (talk) 22:01, 3 August 2014 (UTC)
- Only the humans presence stops the wolf eating the goat, or the goat eating the cabbage. --Pudder (talk) 12:11, 31 October 2014 (UTC)
I've always heard this as a dog-chicken-corn problem. 184.108.40.206 (talk) (please sign your comments with ~~~~)
This is the only website I've heard call it "wolf-goat-cabbage". Even wikipedia doesn't call it that anymore. And the trope is http://tvtropes.org/pmwiki/pmwiki.php/Main/FoxChickenGrainPuzzle - 220.127.116.11 04:35, 22 July 2017 (UTC)