This is Part 10 of a series covering the basics of articulatory phonetics, the study of how humans physically produce speech sounds. For the full list of posts, see the Articulatory Phonetics 101 Index.
What’s the difference between vowels and consonants?
For now, I’m going to give you an answer that might sound quite lame or unsatisfactory. Remember that consonants are formed by creating an obstruction or constriction in the airflow in the vocal tract.
Well, vowels are produced with an open vocal tract. It’s open in the sense in that there is no obstruction, no closure or turbulence in the vocal tract.
Yeah, I know what you’re thinking. What about approximants like /j/ and /w/? There’s no closure or turbulence there, either. Well, the answer is that approximants create more of a constriction in the vocal tract than vowels do. That’s it. Or at least that’s our working definition.
Describing vowels: height and backness
Okay, so now we’ve decided what vowels are. Next question: How do we distinguish one vowel from another? I mean, /i/ (as in “feet”), /ɑ/ (as in “fart”), /u/ (as in “food”) are all vowels, but they’re all different vowels. What makes one vowel different from another? Well — here, I’m going to give a technically incorrect but still very useful definition.
Say /ɑ/, “ahhhh”, like you’re at the doctor. Your vocal tract looks approximately like this (the red dot indicates the highest point of the tongue):
Okay, say /æ/ like the vowel in “ash”. Now, your vocal tract looks approximately like this:
Got it? Now say /u/. This time, your vocal tract looks something like this:
And finally: say /i/. Now, this is what your vocal tract looks like:
We’re going to define vowels based on the highest point of the tongue. So, in /ɑ/, the tongue is low, and the highest point is pretty far back in the vocal tract. In /æ/, the highest point of the tongue is still low, but now it’s much further forward. In /u/, the highest point of the tongue is way up there, and it’s at the back of the vocal tract. And finally, in /i/, the highest point of the tongue is high up here and it’s far forward, almost touching the palate.
These four vowels mark the extremes of what we call the vowel quadrilateral:
Now, we have two axes here: vowel height and vowel backness. Vowel height is how high the highest point of the tongue is, and vowel backness is how far back the highest point of the tongue is.
(A quick but necessary aside for readers with a prior background in linguistics, who may disagree with the choice of low front vowel: Why /æ/ and not /a/ for low front, as the IPA chart suggests? See Ladefoged and Johnson, A Course in Phonetics, 6th Edition (Boston: Wadsworth Cengage, 2010): /æ/ is a little higher and fronter, /a/ is a little lower and backer.
The vowel quadrilateral is an abstraction. What goes in the low front position that best fits our model? It seems to me that if you want to emphasise the frontness of the low front vowel, that spot should go to /æ/, and /a/ should be considered a low central vowel. If you want to emphasise the lowness of the low front vowel, then the low front vowel should be /a/ and /æ/ is raised (and fronted) relative to /a/.
As far as I can tell, /æ/ is lower than /a/ is fronted, and so it makes sense to me to put /æ/ in the low front position, and /a/ in a low central position. Also, this is the way I was taught, so I’m sticking to it out of habit.)
Back vowels in English
Try this: say these vowels aloud.
/ɑ/ as in “father”, /ɔ/ as in “all”, /o/ as in “pole”, /ʊ/ as in “pull”, /u/ as in “pool”.
Do you feel the back of your tongue rising towards the top of your mouth? These are all back vowels, but they vary in height.
/ɑ/ is a low back vowel, /ɔ/ is a low-mid back vowel, /o/ is a high-mid back vowel, /ʊ/ is a high back lax vowel, /u/ is a high back tense vowel.
“Well, technically, that’s not the whole story…” — don’t yell at me, I’m trying to keep things simple.
You might also notice that your mouth went from mostly open to mostly closed, so for this reason we sometimes use “open” and “close” to refer to vowel height — but as far as we’re concerned here, we’ll stick with high and low.
We can fill these vowels in our vowel quadrilateral right now:
Front vowels in English
Okay, now let’s look at front vowels. Say these vowels out loud:
/æ/ as in “sat”, /ɛ/ as in “set”, /e/ as in “cake”, /ɪ/ as in “sit”, /i/ as in “seat”.
It’s the same thing here — this time, you’re moving the body of the tongue higher in the vocal tract, and at the highest point the tongue almost — but not quite — touches the hard palate. Using the same set of distinctions we used for the back vowels, we get:
/æ/, the low front vowel, /ɛ/, the low-mid front vowel, /e/, the high-mid front vowel, /ɪ/, the high front lax vowel, /i/, the high front tense vowel.
Our vowel quadrilateral now looks like this:
Mid and central vowels in English
These aren’t all the vowels, though: we also have mid vowels, which are neither high nor low, and central vowels, which are neither front nor back.
Consider the word “fun”: that vowel isn’t as far back or as low as the vowel in “father”. It’s a low-mid central vowel, and it’s written /ʌ/. (Note: This corresponds to what I was taught, not to the IPA, which characterises this vowel as a low-mid back unrounded vowel. There’s a case to be made for either description, but /ʌ/ makes more sense to me analysed as a central vowel.)
Then, there’s the vowel in “bird”. Depending on how you speak, this is either a /bɜd/ (if the vowel has no r-like sound) or a /bɝd/ (if the vowel has an r-like sound). The little squiggle in /ɝ/ indicates that it’s an r-coloured vowel, or rhotacised vowel. For our purposes, we’re going to consider /ɜ/ a mid central vowel.
Okay — now, let’s take a look at the final vowel in “father”.
It sounds the same as the vowel in “bird”, but it occurs in an unstressed syllable. For reasons we’re not going to go into in great detail right now, this unstressed vowel, also a mid central vowel, has a different symbol: /ə/, or /ɚ/, depending on whether your vowel is rhotacised or not.
Now, of these central vowels, it’s worth pointing out that many, maybe most native English speakers won’t use all four of these vowels. Received Pronunciation, or the so-called “BBC English”, doesn’t have /ɝ/ and /ɚ/, and General American doesn’t have /ɜ/. But no matter what variety of English you speak, you will have the vowel /ə/, which is the single most common vowel in the English language. This is the mid central vowel, better known as the schwa. The schwa is the vowel produced when the vocal tract is in a completely relaxed position.
Well, what’s the difference between /ɜ/ and /ə/, or between /ɝ/ and /ɚ/? It’s simple: if the vowel is stressed, we call it /ɜ/ or /ɝ/, and if it’s unstressed, we call it /ə/ or /ɚ/ (depending on the word and on your dialect, of course). Now, the reasons for this have more to do with phonology than with phonetics per se, so we’ll leave it at that.
We’re almost — almost — done with vowels, but there’s one more thing we need to talk about. You might have noticed that when you said /ɑ ɔ o ʊ u/, your lips ended up sort of rounded and puckered, while the front vowels /æ ɛ e ɪ i/ didn’t have the same effect. Well, in most languages, back vowels tend to be rounded, while front vowels tend to be unrounded, but that is only a tendency.
If you speak French or Dutch or German or Mandarin, you might be wondering about the vowel /y/, which in French and Dutch is written <u>, and in German as <ü>, and in Mandarin Hanyupinyin romanisation as either <u> or <ü>. That is a high front rounded vowel. If you say /i/ and round the lips, you get /y/. This vowel exists in tense and lax forms as well, and they’re written /y/ and /ʏ/ in IPA respectively. When you’re writing IPA symbols on a vowel quadrilateral, the symbol for the unrounded vowel always goes on the left, and the symbol for the rounded vowel on the right.
Similarly, there’s no reason the back vowels need to be rounded. You can take /u/, and without moving the tongue, relax the lips, so that they become unrounded, and that’s the high back unrounded vowel /ɯ/. You can take /o/, and again without moving the tongue, unround the lips to get /ɤ/, which is a vowel that exists in Mandarin: that’s the vowel in 喝 hē, “to drink”.
This gives us enough information to fully fill out our vowel quadrilateral:
Okay, I lied — let’s squeeze in one more thing. If you’ve ever tried to learn French or Portuguese, you might have heard of nasal vowels. In French, <bien> isn’t pronounced /bjen/ as it is in Spanish; it’s instead pronounced /biõ/, with no /n/ at the end of the syllable.
Well — in a nasal vowel, the velum is lowered, which allows air to escape through both the nose and the mouth, and that’s what makes nasal vowels sound different.
Nasal vowels aren’t indicated on the vowel quadrilateral. Instead, in order to indicate a nasal vowel, we draw a tilde ~ above the vowel.
Whew. That’s all for now — if you made it through this post, you now know the basics of how vowels are articulated. In the next post, we’ll look at vowel sounds like “eye” /aɪ/, “ow” /aʊ/, and “oi” /ɔɪ/, and how they’re different from the ones we’ve seen so far.