ARTHUR: Actually, I think he might.
MARTIN: No, Arthur, he won’t.
ARTHUR: Hmm. The thing is, though, Skip, with all due respect, but what I’ve got that you haven’t is that Mum sent me on a course on understanding people in Ipswich.
MARTIN (slowly): And if I ever want the people of Ipswich understood, you’ll be the first person I call. Meanwhile…
This is a bit of dialogue from the highly entertaining BBC radio drama, Cabin Pressure, in this case pitting Arthur, the clueless flight attendant, against Martin, the not-especially-captain-y captain. But what I'm really interested in here is where the humor comes from in this passage: The funny business going on around "people in Ipswich" is an excellent illustration of a linguistic phenomenon called structural ambiguity.
There are other types of ambiguity: lexical ambiguity, when a word could mean several different things ("I'm going to the bank (of the river/of commerce)"), and scopal ambiguity, such as "Everyone loves someone" (Does everyone have someone to love, or is there one lucky person who's loved by all?), but the structural kind involves the same sentence having two or more meanings, depending on which words are more closely associated with each other. The idea is that it's not just the linear order of words in a sentence that matters. Even in the same order, whether words are interpreted as part of the same group or different ones can give rise to different meanings. The classic example of structural ambiguity is:
They talked about sex with Dick Cavett
If Dick Cavett is a bit of a dated reference for you, you can of course replace him with Jimmy Fallon or any other host you like. You can even talk about sex with multiple people, if, say, you're a fan of Live! With Kelly and Michael. But the point remains the same. Let's put brackets around the parts that are associated with each other for the two possible interpretations:
[ talked about sex ] with Dick Cavett Intended
talked about [ sex with Dick Cavett ] Innuendo
It's most probable that "sex" is the object and "with Dick Cavett" a mere adjunct, i.e. that the guest was talking about sex while fully clothed on Dick Cavett's show (option 1), but the humorous misinterpretation is that "sex with Dick Cavett" is the entire object, i.e. that the guest talked about Dick Cavett as a sexual partner, although not necessarily in his presence (option 2).
Another type of structural ambiguity occurs with words that can have multiple parts of speech, which also comes with a classic example:
Time flies like an arrow; fruit flies like a banana.
The story goes that when the simple-looking phrase "time flies like an arrow" was given to an early computer parser, it returned far too many possible meanings, ranging from "time proceeds the way an arrow proceeds" to "measure the speed of time the way you'd measure the speed of an arrow" and yes, even "flies of a particular kind, time-flies, are fond of an arrow."
Time flies (verb) like (preposition) an arrow.
Fruit flies (noun) like (verb) a banana.
So what about Cabin Pressure? Hapless Arthur is a victim of that first type of structural ambiguity: What he means when he says "Mum sent me on a course on understanding people in Ipswich" is that it was a course on understanding people in general, and it happened to be held in Ipswich. But Martin misinterprets him, probably deliberately, to be saying that he took a course only for understanding Ipswich-dwellers, thereby allowing him to dismiss Arthur's opinions on the behavior of a non-Ipswichian passenger.
[ course on understanding people ] in Ipswich Arthur's intention
course on understanding [ people in Ipswich ] Martin's interpretation
Martin's interpretation is unlikely, but that's merely a matter of context. If we change the words slightly to "a course on understanding people in relationships," the course is likely to be about, say, the dynamics of dating rather than located in a place called Relationships. And this points to one of the reasons that real-life examples of structural ambiguity are actually quite rare outside of headlines. Unlike computers, we can generally make use of context, common sense, and real-world knowledge to tell us that people in Ipswich are no more difficult to understand than people anywhere else. Or so I assume. After all, unlike Arthur, I've never taken a course on understanding them.