This was originally published in my work Slack on 2016-10-07—and, in fact, looks like an expansion of the first one I ever wrote, but I’m keeping them both for completeness’s sake—but I’ve since been convinced that more people than just those few who can even read it there might be interested. I’ve edited it for clarity and correctness. I’m going to migrate all my Linguistics Minutes over to my blog and probably post future ones here.

In modern English, we have two different sounds that we spell with “th”. We have the voiceless “th” in thistle and the voiced “th” in this, but they’re both dental fricatives. “Dental”, there, is a way of describing where in the mouth the sound is made (the place of articulation): At the teeth. And “fricative” is a way of describing the way the air flows when you make the sound: Squeezing past a narrow gap at the place of articulation.

This overloading of the spelling means that if you encounter a new word spelled “baracathus”, you have to guess and pray. Native speakers mostly have a solid intuition about where things are voiced and where they’re voiceless, but for folks learning English after growing up, it can be somewhat fraught.

This wasn’t always the case, however. Back in the day, Old English had two separate letters for these two separate sounds. A letter called eth was for the voiced dental fricative and looks like Ð for uppercase and ð for lowercase. A letter called thorn was for the voiceless dental fricative and looked like Þ for upper case and þ for lowercase. So a word like thistle would have been spelled “þistel”. And a word like this would have been spelled “ðes” (vowels are shifty).

“This seems kind of useful,” you might think, “Why would we have stopped using these letters?” Well, the answer is the printing press.

The printing press was invented around 1440 by Johannes Gutenberg in the Holy Roman Empire, which was mostly modern day Germany and Switzerland plus sizeable chunks of all the surrounding modern countries. There is, by the way, a Gutenberg Bible on display at the University of Texas in Austin (where I live). It’s neat and there are a few on display at various locations around the world. Maybe one near you!

They didn’t speak much English in the Holy Roman Empire, and I believe Gutenberg spoke some dialect of German, so early printers didn’t make little blocks with eth and thorn on them.

When printing technology eventually made it’s way to England, these new English printers were at an impasse: There were two letters missing from the alphabet they needed and those letters are used all the time. Just count the number of “th”s in the first paragraph of this post. Counting only times that sequence appears in words it’s 19 and it’s often in important grammar words (e.g. the, this, these, with).

So what to do? Well, they figured they’d better just use another letter. Most of the likely candidates are used too much and would be super confusing, so they had to pick a letter that wasn’t used that often. And, you know, a “y” looks kiiiiiiiiiiiiiiiiind of like a “ð” if you squint real good and maybe have a concussion.

So it became popular in printing to use “y” for what we’d spell today with “th”. And most literate people understood that this is what was going on. It wasn’t until much later that we started useing the two-letter combination of “th” to spell these sounds and by then readers had already been influenced by using a single spelling for the two different sounds, so we don’t have something like “dh” for the voiced dental fricative.

What this means is that when you see a sign that says “Ye Shoppe”, it was never pronounced like it looks like it should be to our modern eyes. It doesn’t say “You Shop”… it says… “The Shop.” And most modern English speakers have been widely misunderstanding our predecedors for our entire lives.