So, how did English end up with these peculiar sounds? Where else in the world can we find them? And why did so many of its closest linguistic relatives, like German and Dutch, kick them to the curb centuries ago? Let’s dive into the fascinating world of dental fricatives.

Meet the Dental Fricatives: /θ/ and /ð/

First, let’s get a little technical. Linguistics has a name for everything, and the “th” sounds are no exception. They are known as dental fricatives. The “dental” part refers to the teeth, and “fricative” describes a sound made by forcing air through a narrow channel, creating friction.

English is special because it has two of them:

• The Voiceless Dental Fricative /θ/: This is the sound in words like think, path, and math. To make it, you place your tongue against your upper teeth and blow air. Your vocal cords don’t vibrate, which is why it’s “voiceless”.
• The Voiced Dental Fricative /ð/: This is the sound in words like that, breathe, and mother. It’s made in the exact same mouth position as /θ/, but this time you engage your vocal cords, creating a vibration you can feel in your throat.

This voiced/voiceless distinction is crucial, and it’s something many learners of English struggle with. But the real challenge for most speakers around the world is making the sound at all.

A Global Rarity: Where in the World?

While dominant in English, dental fricatives are surprisingly scarce. A survey of the world’s languages reveals they appear in less than 10% of them. If you were to spin a globe and point to a random language, the odds are overwhelmingly against it having a /θ/ or /ð/.

So, who are the other members of this exclusive club? The distribution is eclectic and tells a story of shared history and linguistic conservation.

• European Languages: Besides English, you’ll find them in Icelandic (which still uses the old letters þ (thorn) for /θ/ and ð (eth) for /ð/), Welsh (written as ‘th’ and ‘dd’), Greek (theta ‘θ’ and delta ‘δ’), Albanian, and most notably, Castilian Spanish, where ‘z’ and ‘c’ (before ‘e’ or ‘i’) are pronounced as /θ/ (e.g., cinco, zapato).
• Arabic: Standard Arabic prominently features both sounds, represented by the letters ث (thaa’) for /θ/ and ذ (dhaal) for /ð/.
• Other Languages: They also pop up in a handful of other languages, including Burmese and some dialects of Berber languages in North Africa.

That’s a small list for such a big world. What’s even more fascinating is the list of languages that *used* to have them but don’t anymore.

The Case of the Missing ‘Th’: A History of Sound Change

The story of “th” is often a story of loss. Both sounds existed in Proto-Germanic, the ancient ancestor of English, German, Dutch, and the Scandinavian languages. While English (and the geographically isolated Icelandic) held onto them, most of its siblings let them go in a process linguists sometimes call “th-stopping” or “th-fronting”.

The German and Dutch Shift

If you’ve ever studied German, you may have noticed some curious patterns. The English word that is das in German. Think is denken. Brother is Bruder. In each case, the English /θ/ or /ð/ sound corresponds to a German /d/ sound.

This wasn’t an accident. Over centuries, the dental fricatives in the Germanic dialects that would become German and Dutch gradually hardened into “stops” (/d/ and /t/). It was simply easier to pronounce. The tongue, instead of resting delicately between the teeth, made a firm, complete stop behind them. The old letter for the “th” sound, thorn (þ), was eventually replaced with ‘d’ in the writing system to reflect the new pronunciation.

The same thing happened in Dutch: the became de, that became dat, and thorn (the bush) became doorn.

What about Russian or French?

For many other languages, they never had “th” to begin with.

• Slavic Languages (like Russian and Polish): Proto-Slavic, their ancestor, didn’t have /θ/ or /ð/. When encountering foreign words with the sound, they typically substitute it with a /t/, /f/, or /s/. The Greek name Theodoros became Fyodor in Russian.
• Romance Languages (like French, Italian, and Portuguese): These languages descend from Latin, which didn’t use dental fricatives. The Latin spelling ‘th’ (as in theatrum) was just a way to represent the Greek letter theta (θ), but it was pronounced as a simple /t/. This is why French has théâtre and Italian has teatro, both with a hard /t/ sound.

Why Is ‘Th’ So Unstable?

Why do these sounds have such a high turnover rate in the world’s languages? There are two main theories, and they likely work together.

1. Articulatory Difficulty: From a production standpoint, dental fricatives are quite delicate. They require precise placement of the tongue. It’s physically simpler to make a /t/, /d/, /f/, or /s/ sound. Languages, over long periods, often drift toward sounds that require less effort—a sort of linguistic path of least resistance.

2. Acoustic Similarity: The sound of /θ/ is acoustically very similar to /f/ and /s/. The sound of /ð/ is close to /v/ and /d/. Because they sound alike, they are easily confused by listeners and can merge over time. We see this happening in real-time in some dialects of English today. The rise of “fink” for think or “bruvver” for brother in Cockney and Multicultural London English is a modern example of the same historical process that wiped out “th” in German.

The next time you thank someone or talk about the weather, pay a little respect to your “th” sounds. They are not as simple or universal as they seem. They are rare survivors, echoes of an ancient Germanic past that connect English more closely to Icelandic and Welsh than to its nearer cousins, German and Dutch. They are a testament to the weird, wonderful, and ever-changing nature of human speech.