Why don't "tough" and "dough" rhyme? - Arika Okrent

It was June 2010. Inside the Scripps National Spelling Bee, contestants between 8- and 15-years-old wrestled words like brachydactylous and leguleian. Outside, a crowd protested the complexity of English spelling conventions. Indeed, spelling reformers have been around for centuries, advocating for overarching changes to make English spelling more intuitive.

The English language is chock-full of irregularities. One commonly used example of this: take the “g-h” sound from “enough,” the “o” sound from “women,” and the “t-i” sound from “action,” and you could argue that “g-h-o-t-i” spells “fish.” So, how did English get like this? English arose from old Germanic tribes that invaded the British Isles more than 1,500 years ago. Their languages coalesced and evolved into Old English.

When Roman missionaries arrived around 600 CE, they devised ways to write it down using the Latin alphabet, supplementing it with some Germanic runes for sounds they didn’t have letters for. Then came the Norman invasion of 1066 when French speakers conquered England. French became the language of authority and high society. But English remained the dominant spoken language.

Over time, those descended from French speakers also became English speakers, but some French words snuck into the language. Some English speakers were also familiar with Latin through the church and formal education. By the mid-1400s, people were writing in English again—but it was unstandardized. They used a mix of influences to determine word choice and spelling, including the French they knew, the Latin they studied, and the English they spoke. So, things were already pretty messy.

Then, in 1476, the printing press arrived in England. Some of the people working the presses may have mainly spoken Flemish—not English. And they were given manuscripts that varied widely in their spelling. Without standardization, different writers went with various spellings based in part on what they happened to encounter while reading. Many words had a multitude of spellings. The word “dough,” for instance, used to be spelled in all these ways and was originally pronounced “dach.”

The guttural Germanic sound it ended with was one the Latin alphabet didn’t cover. It eventually came to be represented with “g-h.” But, for some “g-h” words, English speakers eventually dropped the guttural sound altogether; for others, they ended up pronouncing it as “f” instead, as exemplified in “dough” versus “tough.” Printing presses memorialized the spelling even though the pronunciation eventually changed. And this wasn’t just the case with “g-h.” Some letters in other words also fell silent: words like knife, gnat, and wrong all contain the vestiges of past pronunciations.

But while the printing press was solidifying spellings, the English language was also undergoing what scholars call the Great Vowel Shift. Between the 14th and 18th centuries, the way English speakers pronounced many vowels changed significantly. For instance, “bawt” became “boat.” This displaced the word for “boot,” which had up until then been pronounced “boat,” and pushed it into the high “u” vowel position it maintains today. Words that already had this high “u” often became diphthongs, with two vowels in a single syllable. So, “hus” became “house.”

As with so many linguistic matters, there's no clear reason why this happened. But it did. And how the vowel shift affected a word depended on various things, including the other sounds in the word. The word “tough” was once “tōh,” among other variations. “Through” was once “thruch” and “dough” “dah.” These words all started with different vowel sounds that were then affected differently by the vowel shift. The “o-u” spelling they all adopted was a haphazardly applied French influence.

So, eventually they wound up with still distinct vowel sounds, but similar spellings that don’t really make much sense. All this means English can be a difficult language for non-native speakers to learn. And it reveals the many ways history, in all its messiness, acted upon English, making it especially tough.