TH Sounds in IPA: /θ/ and /ð/ Explained

You say think and a listener hears sink. You say this and it comes out closer to dis. Or you get the tongue in the right place and still can't tell whether with or thought should buzz.

English writes two different sounds with the same two letters. The IPA keeps them apart: /θ/ is the voiceless sound at the start of think, and /ð/ is the voiced sound at the start of this. This guide shows how to make each one, the spelling patterns that tell you which one a word takes, and the three substitutions that turn one English word into another.

Two Sounds, One Spelling

Phonetically, /θ/ and /ð/ are a matched pair. Both are dental fricatives: the tongue tip rests at the upper front teeth and air is pushed through the narrow gap, which makes a soft hiss. The only difference is voicing. For /θ/ the vocal folds stay apart; for /ð/ they vibrate.

The symbols have their own story. θ is the Greek letter theta. ð is eth, a letter the IPA took from the Old English and Icelandic alphabets. Old English scribes used eth and thorn (þ) interchangeably for both sounds, because at the time they were two variants of one sound. When th replaced those letters, it inherited the same ambiguity.

Every word transcription in this post comes from a pronunciation lexicon IPAtics maintains and is copied as it is: its American entries put the stress mark before the stressed syllable (ˈθɪŋk), and its British entries mostly leave stress unmarked.

To hear both sounds in real words, the pages for the voiceless dental fricative /θ/ and the voiced dental fricative /ð/ play a set of example words for each.

How to Make /θ/

1. Put the tip of your tongue lightly against the back of your upper front teeth, or just between your upper and lower teeth. Both positions are normal; in Received Pronunciation the tip often sits between the teeth.
2. Leave a thin gap and blow air through it. You should hear a soft, flat hiss, much quieter than /s/.
3. Keep your voice off. With your fingers on your throat, you should feel nothing buzz.

The word that matters is fricative: the air never stops. You can hold /θ/ for two seconds, the same way you can hold /s/ or /f/. If the sound comes out in one short pop, your tongue sealed the gap and then released it, and what you made was /t/.

Practice /θ/ at the start, in the middle and at the end of a word. The end is where clusters build up: in month it follows /n/, and in eighth the /t/ of eight comes first, so you release a /t/ straight into /θ/.

How to Make /ð/

/ð/ uses the same tongue position and the same gap, with the voice switched on. The easiest way in is to hold a long /θ/ and then start humming without moving anything. The hiss turns into a buzz. Your fingers on your throat now feel vibration, and with a finger in each ear you hear the sound hum inside your head.

Like /θ/, it is a gentle sound. Most of what a listener hears is the voice, with only a little friction, and between vowels, as in other, it is often very light. Learners who push hard to make it audible tend to press the tongue into the teeth and end up with /d/. Keep the contact soft.

Which TH Is It? Five Spelling Patterns

The spelling never marks the difference, but the choice is far from random. The patterns below follow Wikipedia's article on the pronunciation of English ⟨th⟩, which also explains where each one comes from.

1. Grammar words take /ð/ at the start

A small, closed group of function words starts with /ð/: the article the; the demonstratives this, that, these, those; the pronouns they, them, their and the old thou, thee, thy; and the adverbs and conjunctions there, then, than, thus, though.

Nearly every other word that starts with th takes /θ/. Nouns, verbs and adjectives such as think, thing, three, thumb and theory all begin with the voiceless sound.

The reason is historical. In Old English, the voiced sound was only a variant that appeared between two voiced sounds, and every word that started with th started with /θ/. The grammar words are almost always unstressed and run straight on from the word before them, and in Middle English they came to be said with /ð/, possibly because they took on the voicing of the sounds around them.

2. Between vowels: /ð/ in everyday words, /θ/ in Greek ones

In native English words, th between vowels is usually /ð/: father, brother, weather, together. Words borrowed from Greek, usually by way of Latin, mostly kept /θ/ in the middle of the word: method, athlete, cathedral, marathon. A practical test: if the word sounds learned or technical, try /θ/ first.

The main exception runs the other way. Words ending in -thm, such as rhythm and algorithm, have /ð/.

3. At the end: nouns take /θ/, verbs take /ð/

A final th in a noun or adjective is usually /θ/. In a verb it is usually /ð/, and the verb often adds a silent e.

In the first two pairs the vowel changes as well, so breath and breathe differ in more than voicing. Old English explains this one too: the verbs once had an ending after the th, which put it between vowels and voiced it. The ending disappeared and the voicing stayed.

4. Plurals and related words can switch

Some nouns that end in /θ/ switch to /ð/ in the plural, and some do not. There is no reliable rule, and Wikipedia's article notes that a few plurals, mouths and paths among them, are heard both ways.

Related words behave just as unpredictably. South has /θ/ but southern has /ð/, and worth becomes worthy with /ð/, yet health and healthy both keep /θ/. Learn these as pairs.

5. Sometimes th is not a TH sound at all

In a handful of names, and in the herb thyme, th is a plain /t/. In compounds, the t and the h belong to different parts of the word, so you say /t/ and then /h/.

/θ/ vs /ð/: The Few Minimal Pairs

Because the patterns above are so regular, English has only a handful of word pairs in which /θ/ against /ð/ is the only difference. Loath and loathe from the table above are one. Thigh and thy are another.

The small arch under ɪ in the British entry for thy only marks the second half of the diphthong; the vowel is the same as in thigh.

In American English, ether /ˈiθɚ/ and either /ˈiðɚ/ are a pair as well. British speakers who say either with the vowel of eye don't have that one.

Thy is archaic, which tells you how little work this contrast does: it almost never separates two everyday words. Mixing up /θ/ and /ð/ still sounds wrong to a native ear, but it rarely changes the meaning. The substitutions in the next section cost more, because they produce different, real words.

The Three Common Substitutions: /t d/, /s z/, /f v/

Wikipedia's article on the voiceless dental fricative calls /θ/ "rather rare as a phoneme among the world's languages", so many learners have never had to make these sounds. They replace them with a nearby sound they already have, and the replacements fall into three families. Each one comes from a different thing going wrong in the mouth. (Arabic speakers are the exception: both sounds are letters of the Arabic alphabet, as English pronunciation for Arabic speakers explains.)

/t/ and /d/: the tongue stops the air. If the tongue presses against the teeth and seals the gap, air builds up behind it and bursts out. /θ/ becomes /t/ and /ð/ becomes /d/: thought turns into taught, then into den, though into dough. The fix is to hold the sound. A /θ/ you can stretch for two seconds is a fricative; one you can't stretch is a stop.

/s/ and /z/: the tongue pulls back. If the tongue tip retreats behind the teeth to the ridge above them, the soft hiss sharpens. /θ/ becomes /s/ and /ð/ becomes /z/: thick turns into sick, breathe into breeze. The fix is a mirror. On /θ/ and /ð/ you should see the tip of your tongue at the edge of your teeth. On /s/ you see no tongue at all.

/f/ and /v/: the lip does the work. If the lower lip rises to the upper teeth, the tongue is no longer needed, and you get /f/ and /v/: thought turns into fought, death into deaf. The fix is to keep the lower lip down and away from the teeth. Spreading the corners of the mouth slightly, as if starting a smile, helps keep the lip out of the way.

Native speakers make some of these swaps too. Saying /f/ and /v/ for the TH sounds, known as TH-fronting, is a well-known feature of London English, and stops in place of the fricatives are typical of Irish English; J. C. Wells describes both in Accents of English, vol. 2, The British Isles (Cambridge University Press, 1982). Jennifer Jenkins's Lingua Franca Core, a proposal for what speakers of English as an international language need to stay intelligible to one another, leaves /θ/ and /ð/ out and accepts substitutes (The Phonology of English as an International Language, Oxford University Press, 2000).

So a substitution rarely stops communication. It is a question of which accent you are aiming for. If your target is General American or standard British English, the TH sounds are part of it.

A Short Practice Routine

1. Hold /θ/ for two seconds, then switch on your voice to get /ð/. Repeat five times without moving your tongue.
2. Read one block of the substitution table aloud, such as thought, taught, sought, fought. Record yourself and check that the first word sounds clearly different from the other three.
3. Practice the grammar words in phrases, because that is where /ð/ turns up most often: this and that, the other one, with them. Then mix the two sounds: they think and this thing put /ð/ and /θ/ side by side.
4. When both sounds hold steady, move on to the /θ/ against /s/ pairs and the other contrasts in English minimal pairs that learners confuse.

In running speech, the is usually weak, with a schwa for its vowel, as the dictionary entry shows. The guide to the English schwa explains why grammar words shrink like this and how to hear it.

Frequently Asked Questions

What is the IPA symbol for "th"?

English th stands for two IPA symbols: /θ/ (theta) for the voiceless sound in think, and /ð/ (eth) for the voiced sound in this. In a few names, such as Thomas, it is a plain /t/.

Is the "th" in "with" voiced or voiceless?

Both are heard. Wikipedia's article on English ⟨th⟩ gives /θ/, the original pronunciation, as the northern British form and /ð/ as the southern one, and American dictionaries list both. The lexicon behind this post gives /ð/ in its American and its British entry.

Is the "th" in "thank you" voiced?

No. Thank is a content word, not a grammar word, so it starts with voiceless /θ/, like think. Keep the tongue at your teeth and the air flowing, or it drifts toward tank or sank.

Trying It Yourself

The fastest way to learn which TH a word takes is to check each new word as you meet it, until the patterns above run on their own. IPAtics shows the IPA for any text you select, in any app, so that check takes a second. In the browser, the IPA translator does the same for text you type in.