Why four and five shouldn't exist

     The words ‘four’ and ‘five’ were never supposed to be ‘four’ and ‘five’. They should have been ‘whour’ and ‘figh’.

     Ok, that might an odd way to put it. Let me explain. Most European languages are genetically related, in that they descend from a common proto-language. Linguists can find a lot of cognates (words in different languages descended from a common proto-word) among these languages, but words’ meanings tend to change over time.

     The words for numbers tend not to shift in meaning as much, though, so they often provide easy examples of sound change. Let’s look at words for 6 across different European languages:

German sechs (pronounced zeks)

Dutch zes (pronounced zayss)

French six (pronounced seess)

Spanish seis (pronounced sayss)

Greek έξι (pronounced eksee)

Persian شش (pronounced sheesh).

Also compare Spanish uno with ‘one’, Albanian nëntë with ‘nine’, and Lithuanian septyni with ‘seven’.

     Fascinating. But it’s hard to see any kind of sound connection between four and cuatro or quatre, and between five and cinco or cinq (Spanish and French, respectively). Why's that?

To explain it, we have to look at the ancient forms of these words—the words that transformed into four, cuatro, quatre, five, cinco, and cinq. Linguists had to reconstruct these words, since the ancient language was never written down. And they came up with kwetwores for ‘four’ and penkwe for ‘five’. It’s maybe easy to see how kwetwores turned into cuatro and quatre, but the other developments are…weird.

     The trick is that sometimes sounds don’t just change into similar sounds. Sometimes they unpredictably change to be more like a nearby sound in a word, or a sound in an associated word; this process is called assimilation. This seems to have happened in the history of English when the ancient form kwetwores became petwor- to be more like penkwe. They were associated because they’re always said together in counting. So what if that assimilation had never happened?

     The history of the word would have mostly remained the same, except that the sound at the beginning, originally [kw], would have turned into [hw]. Think of Spanish que and English what, or quiet, which comes from Latin, and while. But the [hw] sound isn’t found much in English today—it’s mostly turned into either [w] (like in white, wheat, and what), or [h] (like in whole, whooping, and who). Notice that [hw] became [h] only before [o] and [u] sounds. Therefore, four should have been whour, pronounced originally as [hwor], but later pronounced the same as whore.

     Okay. How do cinco and five both come from penkwe? More assimilation. This time, it happened in the history of both English and Spanish. In English’s ancestor, the [kw] became [p] under the influence of the [p] that was already at the beginning of the word. Result: penpe. Next, the [n] assimilated to be like the [p]. Result: pempe.

The order of these changes matters a lot for the history of some words, but for these examples it doesn’t matter too much. A few changes later, we get fimf. [p] often turned into [f] in English’s past. Think of pisces, the fish, from Latin, and fish, or pedal, also from Latin, and foot. Later, all [m] and [n] sounds disappeared before [f], [s], [th], and [h] sounds. Result: fif. This was pronounced feef until sometime in the 1400s or 1500s.

     So, if the [kw] had never become [p], the word’s history would have mostly been the same. Judging from what we saw with four, you might expect that we’d get fiwh. And that’s pretty much what happened. [kw] sounds didn’t always become [hw], though—in some places, like here, they became a sound we don’t have in modern English. It’s the scraping sound in the back of the mouth found in Scottish and German, with a [w] after it. Let’s call it [khw]. So we’d have fikhw. Except the [w] would then disappear. Result: fikh. The [kh] sound came to be spelled with ‘gh’, but then it disappeared from English. Sometimes individual [kh] sounds just turned into nothing (like in daughter), and sometimes they turned into [f] (like in laugh). In this case, it would have turned into nothing. Take high as an example. Result: a word spelled figh, pronounced fee in medieval English but fye in modern English.

     And yet, figh isn’t really much more like cinco than five is. But that’s because assimilation happened in the history of Spanish, too. In Spanish, it happened differently. Remember that we start with penkwe. In the ancestor of English, we get penpe, but in the ancestor of Spanish, we get kwenkwe, messing up sound correspondences for everyone. If you know Latin, you might recognize that word as quinque, Latin for ‘five’—like in quintuplets.

     A few other changes then happened. The first [w] sound disappeared, while the second [w] sound became a real vowel: an [o]. At some point, the [e] ending disappeared, giving us a process of kwinkwe -> kinkwe -> kinkoe -> kinko. Finally, the first [k] turned into [s]…but that’s another story.

     So if penkwe hadn’t turned into kwenkwe, we’d have pinco today instead of cinco! It's interesting that even if assimilation hadn't happened, figh and pinco still seem pretty different.