As a field of study, linguistics is a relative newcomer compared to more established social sciences like anthropology and psychology—but you might expect that linguists would have at least agreed where to draw the line between dialect and language. Alas, as always, the reality is much more complex.

If you’re unconvinced, allow me to introduce the Scandinavian languages (language? We’ll see) of Norway, Sweden and Denmark. These three languages lie on what’s known as a dialect continuum, which, if you speak English as a first language, probably won’t be something you’ve encountered before, but it’s integral to understanding why it’s so difficult to discern between a dialect and language.

To start, we need to define mutual intelligibility—a term used to refer to the ease with which two speakers can understand one another. For example, someone from Sydney and someone from Hobart have high mutual intelligibility in their speech, as their varieties of English are nearly identical. To contrast, that Sydneysider and a German speaker have low mutual intelligibility, owing to the fact that English and German have been evolving separately as languages for thousands of years. Mutual intelligibility is one of the main parameters used to discern a language from a dialect.

Now on to dialect continuums, which I’ll illustrate with a hypothetical scenario: let’s say there are two towns, town A and town B. Residents of town A speak dialect A, and those in town B speak dialect B. These dialects have a high mutual intelligibility. Now imagine there is a third town, called town C, which is located near town B, but further away from town A. People from town C speak—no points for guessing—dialect C, which also has a high mutual intelligibility with dialect B. But dialect A and dialect C? They’re spoken by people who live so far away from each other that pretty significant changes have happened over time. Keep in mind—both dialects can be understood pretty well by speakers of dialect B.

I’m sure you can see where this makes identifying what a language is a very difficult task—do the people from towns A, B and C all speak the same language? It would seem not, based on the parameter of mutual intelligibility. So where do you draw the line? How do you split these dialects into languages in a way that sufficiently accounts for the differences between them, but without drawing arbitrary distinctions based only on geography and not linguistic differences?

As you might have guessed, this arbitrary geographic distinction is basically the situation in Scandinavia; there exists a dialect continuum which can more or less be visualised as spreading from Denmark, to Norway, to Sweden. Norwegians are the hypothetical residents of town B in this scenario: they are the best at understanding the other two languages.

So what’s the go with the division into three languages if they’re on a continuum? Part of it is geopolitics. Though there are plenty of cultural similarities between them, these three nations haven’t ever really been unified. Sweden and Denmark both have their own official standardised languages which are taught at schools and regulated by the government.

The situation is a bit more complex in Norway, which has had political unions with both countries in the past. There are two written standard languages—one of which is really similar to written Danish—and no official spoken standard at all. As a result, it’s never really had a centralised linguistic tradition; regional dialects are still abundant here, and are frequently heard in media. Danish, on the other hand, went through standardisation much earlier than its sister languages; its dialects that were more similar to Norwegian and Swedish dialects have all but been lost, and with them has gone a part of the continuum. It’s probably not surprising, then, that Danes struggle the most with understanding other Scandinavian languages.

There isn’t really a simple way to summarise the nuances of what some term the Scandinavian dialect continuum. There are many other factors, many of which differ from person to person based on exposure to different dialects, and many more of which are based on historic differences. If nothing else, Scandinavia is living proof of two things: the aphorism commonly attributed to Max Weinreich, “A language is a dialect with an army and a navy”; and that countries are basically fake.