The cot-caught merger: a dialectal difference and early literacy instruction

Language is always evolving, with new words (bingeable, superspreader), new expressions (I can’t even), and even shifting syntax (Have you any? vs Do you have any?) and grammar (the fading subjunctive: If I were…).  But the main topic of interest today is shifts in pronunciation.  The way we pronounce words changes slowly over time, often specific to a geographical area or demographic, resulting in a patchwork of different accents among speakers of the same language. 

Pronunciations can sometimes change so much that sounds that were once distinctly different are now pronounced exactly the same.  This is known as a merger. A well-known and wide-spread example of this is the low-back merger, a.k.a. the cot-caught merger, where the vowels in the words cot and caught have evolved so that they are no longer two distinct sounds.  Depending on where you live, you might be thinking one of two things right now: Of course “cot” and “caught” sound exactly the same! or There’s no way that “cot” and “caught” sound the same!  Pretty much all Canadians have the cot-caught merger, while the US population is split between merged and unmerged.  As a result, although the different spellings remain, the vowel sounds in the words cot/caught, nod/gnawed, stock/stalk are identical for some English speakers and not for others.  If you have the cot-caught merger and have a hard time understanding how other people can possibly produce and perceive these as two different sounds, you may like to check out this video.

This is all very interesting, but what’s the application to literacy instruction?  Well, this is an issue that comes up surprisingly often in online forums for literacy and language enthusiasts, including a few times recently in a wonderful community on Facebook called Science of Reading- What I Should Have Learned in College, a group dedicated to sharing knowledge about evidence-based practice in literacyPeople in this group know that a very efficient way to teach kids to read and spell involves having them pay attention to the sounds in their spoken words, and then linking these sounds to the letters of our alphabet.  This approach is aptly called speech to print. 

There are many published materials that help teachers apply the speech to print approach.  A slight issue is that some of them may not discuss dialectal differences like the cot-caught merger.  So, what happens when one of the millions of people who has the cot-caught merger comes across these materials?  Occasionally, some confusion.  Huh, have I been pronouncing these words wrong my whole life?  Am I actually making a barely perceptible distinction between these two sounds?  Should I help my students make/hear a difference between these sounds?  Thankfully, the answer is no, no, and no.  If you don’t have the distinction in your dialect, you simply don’t have it, because they are the same sound.

If you are one of the millions of speakers with the low-back merger, you don’t need to toss out great instructional materials that differentiate between these sounds.  We just need to understand the phenomenon, so that we can treat the o in fox and the aw in saw as two different graphemic representations of the same sound, without trying to force a distinction that just isn’t there.  If you speak a dialect with the cot-caught merger, the o in fox and the aw in saw are as much the same sound as the ee and ea in tree and treat, which at one time were also distinct sounds that have completely merged for most dialects of English, as of around 300 years ago. 

One precision.  The graphemes for the o and aw/au sounds do not present exactly the same scenario as ee vs ea.  The graphemes ee and ea are both vowel teams: two vowel letters representing one vowel sound, as in meet and meat.  In contrast, o is a short vowel, while aw/au function like vowel teams.  Diving a little deeper, a careful look at English orthography reveals that a number of spelling rules depend on whether a syllable contains a short vowel or vowel team.  For example, we use -ck at the end of a short word following a short vowel, as in rock, while the word hawk requires only -k after the vowel team aw. So, even if they sound the same for you, it probably makes sense to clearly differentiate short o from vowel teams au/aw because it helps us make sense of spelling patterns. As a Canadian, if I were making a sound wall to help children understand the sounds of English, I would put o and aw/au stuck right together, side-by-side, and I would of course pronounce them exactly the same.

From Speech to Print: Language Essentials for Teachers by Louisa Moats. The cot and caught vowels are differentiated in this chart (fox and saw), though the book discusses dialectal differences. Other spellings for o/aw/au are also shown.

Just to complicate things a little further, not all speakers who have distinct vowels for cot and caught divide these two sounds the same way.  The Atlas of North American English (Labov et al, 2006) explains that in certain contexts, mainly before the voiceless continuant sounds /f, s, th/ (as in off, loss, cloth) and before the /g/ sound (as in dog, frog), words with the short o are actually spoken with a vowel closer to the sound heard in saw/caught.  Hence, hot-dog actually has two different vowel sounds for some speakers, because of the influence of the consonant sounds at the end of each syllable.  Isn’t phonology interesting?? 

So, what do you do if a curious young mind notices that the o and aw/au are represented by different pictures or gestures, or appear as different on the vowel sound chart, and yet have the same sounds?  Rather than give the all-too-common response “English is complicated!  That’s just how it is!”, you could see it as a neat opportunity to introduce dialect differences and language change: “Some people pronounce these differently, but for us they are the same.” 

Does this seem a little complicated? Like very many aspects of literacy and language, the underlying ideas are pretty complex, but that doesn’t mean that it needs to be for children. Doctors have oodles of deep knowledge that informs their sometimes simple advice to patients. Similarly, when educators understand the complexities of our language- both the oral and the written systems- they are in a much better position to teach it to young learners, using simple explanations adapted to the children’s needs and capabilities.

I love this topic, because it is a great example of how there is so much knowledge to be shared when people from a variety of backgrounds- speech pathology, education, linguistics, psychology- come together to look at practices in literacy. Does this sort of knowledge float your boat, bake your cake, rock your socks?  You will no doubt love Speech to Print: Language Essentials for Teachers by Louisa Moats, a comprehensive resource about the oral language underpinnings of literacy development.


Labov, William & Ash, Sharon & Boberg, Charles. (2006). The Atlas of North American English: Phonetics, Phonology and Sound Change. 10.1515/9783110206838.

Moats, L. C. (2020). Speech to print: Language essentials for teachers, 3rd ed. Baltimore: Paul H. Brookes Pub.

One thought on “The cot-caught merger: a dialectal difference and early literacy instruction

  1. A friend who grew up in CA insisted that “tot” and “taught” sound exactly the same; I grew up in CT and they are obviously different. How could this be? Thank you so much for clearing up this mystery! Completely fascinating! We are both academics but not in this field. I appreciate you!

    Liked by 1 person

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