As we’ve covered on our blog before, it’s not always easy to distinguish between a language and a dialect. One criterion that can help differentiate between the two is mutual intelligibility. That means whether two speakers can understand each other without spending time and energy on learning each other’s language. Ideally, dialects should be mutually intelligible, whereas languages are to remain unintelligible. However, even here the distinction is not easily made, as sometimes the speaker of one tongue can grasp the meaning of another, while the other speaker struggles.
This is the difference between symmetric and asymmetric intelligibility.
With symmetric intelligibility, everything is as it should be with mutual understanding. Speakers of two (possibly somewhat distinct) languages or dialects are able to understand each other without many problems. You can consider, for example, the different varieties of English. Although there might be pronounced differences in pronunciation and vocabulary, speakers of South African and Irish variants do not have to struggle too much to understand each other. This is (although there are naturally other reasons, too) why we can say they both speak English.
However, things get a little bit more complicated when we start taking into account various dialect continuums. A dialect continuum is essentially a geographical area, where the language spoken differs only slightly between neighbouring areas, but the differences accumulate to an extent where the opposite ends of the spectrum become unintelligible to each other. For example, this is very similar to what happens in Central Europe, with speakers of Polish, Slovak, and Czech.
This is still somewhat different from asymmetric intelligibility.
Even with problems of understanding rising from dialect continuums, the issues are rather evenly distributed between the two speakers. With asymmetric intelligibility, however, the speaker of one language or dialect can understand the speaker of another much more readily than vice versa.
There are many reasons for why this could happen. One example is the difference between Dutch and Afrikaans. Afrikaans is a direct descendant of Dutch, but it has also simplified its grammar. This makes it easier for Dutch speakers to understand Afrikaans than the other way around. A classic example is also the set of North Germanic languages in Scandinavia where the speakers of Danish, Swedish, and Norwegian variably struggle with understanding each other.
Other times, cultural factors come into play. For example, in many cases, the speakers of one variation of a language or dialect have been exposed to the other much more than vice versa. Many Estonians have grown up watching Finnish television and hearing tourists from the bigger neighbour in their country, which makes it easier for them to grasp Finnish. Finns have enjoyed no such exposure and, as such, struggle more.
Additionally, it is sometimes difficult to draw a distinction between natural intelligibility and simply knowledge of another language. Take the dialects spoken in the Austrian Alps or Switzerland – everyone from those regions understands Hochdeutsch, while it hardly works the other way around. The same issue of confusing a lingua franca for intelligibility could be said to take place between Russian and Ukrainian or Russian and Belarussian.
As with many things in linguistics, it’s hard to draw very concrete lines between different types of understanding. From symmetric (or mutual) intelligibility, where speakers of two dialects or variants understand each other with ease, to the issue of dialect continuums, and finally asymmetric intelligibility, the business of characterising languages and dialects is a muddy one. Sometimes cultural and exposure factors make it even harder to distinguish between what is naturally understood and what is acquired through necessity.