(part of the occasional series What is a joke?)
Almost every joke relies on background knowledge, something that the person telling the joke assumes those hearing it already know, and so does not actually state. Indeed, it is often crucial to the success of the joke that this knowledge is left unstated. To include too much information in setting the joke up is either to risk confusing the audience or to lose the element of surprise which the punchline requires. Hence, the classic way to kill a joke is to explain this background knowledge, though of course this fact has become such a staple of comic lore that it is ripe for comic use itself.[i]
A good number of jokes not only assume this background knowledge but exploit it – it is often crucial to a misdirection which is reversed, or in establishing the connection between the setup and the punchline. (For instance, the hoariest of ‘and that was just the teachers!’-style humour relies on our knowing how teachers typically act, in order to undercut this assumption).
The background knowledge is sometimes very general (jokes about the differences between men and women) but it can be much more specific, e.g., limited to knowledge common only to people in a certain social group, profession or nationality. Any joke of this kind is an in-joke: it is intended to be heard by insiders, people who will get the reference or already have the knowledge needed to understand the joke.
One interesting feature of in-jokes is that because they rely on this shared knowledge, they can get a desired response not necessarily by being funny; often, they work as a kind of shared affirmation that the joke-teller and the audience are in the know, that they get the reference or are part of the relevant social group. And yes, this can lead to a certain degree of smugness. But it does raise the question of how an in-joke can actually be funny, as opposed to just amusing those who understand what it’s about.
Here’s an example of an in-joke which is clearly funny: two behaviourists have just finished making love. The first says to the other ‘I know you enjoyed that, but how was it for me?’[ii]
Why is this funny? Well, it’s about sex, which helps; it’s a highbrow riff on a clichéd situation, which is another plus; but basically, it’s funny because it brings out a ridiculous consequence of a particular theory. It presents, in highly exaggerated form, a line of thought which some people have been tempted to follow, and it shows that this line of thought leads to an absurd dead end. In doing this, the joke adds value to the reference: to get the joke, you need to understand what behaviourism is, but in getting it you will also grasp how ridiculous it is (at least in this exaggerated version).
By way of contrast, here’s an example of an in-joke which is undoubtedly clever but not particularly funny: three logicians walk into a bar. The barman asks ‘Does you all want a drink?’ The first logician says ‘I don’t know’. The second says ‘I don’t know’. The third says ‘Yes!’[iii]  
(If you’re not sure what the joke is – and for what it’s worth, it had to be explained to me, which may say something about my aptitude for logic – see below.)[iv] [v]
In fact, I’m not sure if this counts as a joke at all (at least two people who heard it both said the same thing to me). It does follow a well-known jocular format, has the rhythm of a joke (including what looks a lot like a punchline), and relies on the listener making a connection which draws on relevant background knowledge. But what do you get, when you ‘get’ this joke?
It is true that in understanding why the final logician answered as they did, the listener grasps the thought processes behind the first two answers, so there is a leap from the information in the premise to the conclusion; and it is true that in many jokes a similar leap is required to get the punchline. But it is characteristic of jokes that the final piece of information not only throws the rest of the joke in a new light, but reverses or undercuts something (either our understanding of the previous pieces of information, or some assumption which we had been led to make).
I don’t think there is any comic reversal here. (At most, if you didn’t understand why the first two logicians answered as they did, the final answer might have clarified their thinking – but this doesn’t seem like a genuine reversal so much as clearing up something which had seemed confusing or arbitrary.) This a clever connection, and the way you grasp it might be quite like the way you grasp a punchline, but the line itself is more like the answer to a riddle, presented in a joke-shaped format.

[i] Douglas Walker had a great example of this in his Edinburgh show a couple of years ago.
[ii] This joke is aimed primarily at logical behaviourism – see b.ii here.
[iii] Tip of the hat to Vincent for introducing me to this one.
[iv] Each logician either wants a drink or does not. If the first logician did not want a drink, then she would have known that the answer to the barman’s question was ‘No’ (since in order for the correct answer to be negative, all it takes is for one of the logicians to not want a drink). So because she did not answer ‘No’, she must want a drink. But she does not know if either of her colleagues want a drink, therefore she could not answer ‘Yes’, hence her answering ‘I don’t know’. Same goes (more or less) for the second logician. But the third logician, having heard the answers from the first two, deduces that each of them wants a drink (since if either of them had not wanted a drink, they would have said ‘No’). And since the third logician wants a drink, he knows that the answer to the barman’s question is ‘Yes’. QED.
[v] There’s a further issue here with some background assumptions which the joke requires. Specifically, it only works if each of the logicians knows whether or not they want a drink. If it is possible that they do not know this, then the final logician could not conclude that the other two did want a drink, and so would not be in a position to answer ‘Yes’.


  1. With the behaviourism example, whereas I agree with your analysis although I think it misses out the core mechanism that makes that a good joke. Here's how I'd analyse it:

    At a high level it's an example of the joke form: practitioner of x exhibiting x, you can tell straight from the second word "behaviourists" that the joke is probably going to be in this form.

    These types of jokes usually go well with juxtaposing with another idea, in this case sex: so it's x + sex. As it's about sex it's common to make the leap from sex -> x (it's quite a bit harder to come out with a joke that surprises the sex element if you introduce it in the setup). Since sex is such a pivotal concept the joke already fares a bigger chance of being funny to people just by that being one of the two concepts in the juxtaposition.

    The punchline itself "I know you enjoyed that, but how was it for me" works I think critically because it is a comic reversal. Specifically of the expression that usually goes something along the lines of "was it as good for you as it was for me?".

    The fact it's taken an expression related to the concept of sex, reversed it, and that reversal makes sense within the concept of behaviourism is what gives this joke its punch.

    As for the logicians joke, it's also in form: practitioner of x exhibiting x. I would argue it is a joke, but I define at least a subset of jokes on a more neurological level as things that cause two conflicting notions to exist in dissonance before one is replaced by the other.

    In this example, in the first part of the joke it's assumed the first two people do not know whether they want a drink or not - this is the naive reading. In the second part, this is inverted and revealed that they in fact did want a drink, but being particularly logical could not answer under a strict reading of the question posed.

    This joke hinges on the barman saying "do you *all* want a drink" it doesn't work without the word all. It's this shift which causes a reinterpretation of the original "I don't know" that's key to why I would classify this as a joke. Essentially a variation of a paraprosdokian[1] with unsaid being what causes the reinterpretation (due to its logical implication).

    [1] https://en.wikipedia.org/wiki/Paraprosdokian

    I think what makes the joke work is also what prevents the joke from being top tier. It relies on too much work on the part of the reader, given its reliance on the unsaid. It also doesn't juxtapose two concepts like the above joke, sure it's set in a bar but that's just set dressing nothing intrinsic to a bar is juxtaposed in the punchline.

  2. Hi Alex,
    you're right of course that behaviourist joke is funny in part because the punchline is a version of a cliché about sex (that's partly what I had in mind when I mentioned that it was a riff on a clichéd situation, but the comic reversal of the phrasing is important as well).
    Re the logicians joke, that's a fair point about the listener reclassifying the first two answers in light of the third. So it does qualify as an example of paraprosdokian (which I'd never heard of, so thanks for the tip). Whether it counts as a joke depends, I think, on whether the final answer undercuts or reverses the listener's understanding of the first two answers, or merely clarifies it - I thought it was the latter, you think it's the former, and that seems to me to be the crucial question in deciding whether or not to classify this as a joke.

  3. Yes very much so re the classification, good way of putting it.