THE DIFFICULTY in learning a foreign language lies not only in its inherent complexity. Languages are complex in different ways (though all are learnable by infants). The main reason a language is hard is that it is different from your own.

America’s State Department places the languages it teaches diplomats into four categories (see chart), with estimates of how long they take to learn them ranging from 24 to 88 weeks. What underlies the difficulty of such languages for an English-speaker?

The first thing many learners will think of is the writing system. Indeed none of the State Department’s hardest languages is written with the Latin alphabet used by most European languages. Chinese stands out for its difficulty. It is commonly said that a learner must memorise around 2,000 characters to be able to read a newspaper. But even this estimate is criticised; someone with 2,000 characters will still have to look up unfamiliar ones in every few lines of text. Japanese is (mostly) written with a subset of the Chinese characters, but most characters can be given either a Japanese or Chinese pronunciation, making the task mind-tangling in that language too.

But foreign writing systems need not be difficult. The other writing systems in the “hard” category are all quite learnable. Arabic is alphabetic, with just a couple of dozen letters. Its two complications are that letters change shape depending on where they appear in a word (beginning, middle, end or alone) and that short vowels are not written. And Korean’s hangul system is technically a syllabary, in that every character stands for a syllable not a single sound. But hangul is widely admired for being simple and logical.

A second way languages can be hard is with sounds and distinctions that do not exist in the learner’s language. To an English-speaker, the novelties include the clicks of many African languages and the ejective sounds (made by a sudden release of pressure in the mouth) in some Caucasian ones. But just as hard is the problem of languages that make distinctions your language does not. In Hindi, the t- and d-sounds can be “retroflex” (with the tongue curled back) or not, making two different letters that can distinguish two different words (moti with a retroflex t means “fat, thick” and with a non-retroflex t means “pearl”). Mandarin and Cantonese have tones, meaning ma with an even pitch and ma with a falling one are different words. (Mandarin has four tones; Cantonese has more, though the number is disputed.)

The lexicon obviously matters too. Most European languages share an ancestor (called proto-Indo-European) and so their words, too, often come in related pairs. If you know water in Spanish is agua it is easy to figure out Italian acqua and English aquatic. But the European languages share vocabulary for another reason: they have freely borrowed from one another over the centuries. Languages unrelated to the European ones (Arabic from the Semitic family, or Chinese from the Sino-Tibetan one) will not only lack the “genetic” overlap in vocabulary. They are culturally distant, and so have far less borrowed European vocabulary too.

Finally there is grammar. Many people associate tricky grammar with long lists of endings that change according to a word’s use in a sentence. This crops up all over Arabic, in which those changes can also be prefixes, suffixes, or vowels and consonants inserted in the middle of a word. This more than anything else accounts for the difficulty of the language. Mandarin, though, almost entirely lacks such inflection, as linguists call it. Foreign grammar is also difficult to the extent that it makes distinctions your language does not; for example, Arabic has a dual number (where verbs conjugate differently when the subject is two people or things), alongside singular and plural. Many languages even feature an ending on verbs indicating how the speaker knows the information to be true.

The overall hardness of a language can be seen as the sum of the difficulty of its writing system, sounds, words and grammar. These come in different proportions: one professor of Chinese has called it the most difficult language he has ever learned to write and the easiest he has learned to speak.

If you want to learn a language just for fun, start with Swedish. If you want to rack up an impressive number, stay in Europe. But if you really want to impress, bulking up your brain to master Cantonese or Korean is the sign of the true linguistic Ironman. ■