English /θ/ vs /s/
think vs sink: tongue between teeth, or behind them?

One tiny tongue position separates these two sounds. For /θ/, the tongue tip goes between the teeth. For /s/, it stays behind the teeth. That gap -- roughly the width of a tooth -- is all that stands between "I think so" and "I sink so." The /θ/ sound is genuinely rare across the world's languages, which is why so many learners default to /s/ without knowing it.

The ABX drill plays two reference sounds then a mystery sound X. Choose which one X matches. Five rounds is enough to start building a real perceptual gap.

👅Tongue between vs behind teeth
🔇Voiceless fricative pair
🌍Rare sound worldwide
⚠️Very common ESL mistake
Can you hear the difference?
How it works: You'll hear sound A, sound B, then a mystery sound X. Choose whether X matches A or B. Words are revealed after you answer.
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Listen carefully...

Mystery sound

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The problem

Why /θ/ is one of the world's rarest sounds

The voiceless dental fricative /θ/ appears in fewer than 450 of the world's 7,000+ languages. English, Modern Greek, and a handful of others have it. That's it. When speakers of Spanish, Mandarin, Japanese, Portuguese, or Arabic encounter /θ/, they have no existing phoneme to map it to -- so they grab the closest thing: /s/.

The acoustic similarity makes it worse. Both /θ/ and /s/ are voiceless fricatives -- continuous, hissing sounds produced without vocal cord vibration. Without careful listening, they can sound nearly identical, especially in fast speech or over the phone.

There's also a visual problem: you can't watch someone's mouth and easily tell whether their tongue is between or behind their teeth. The movement is small. This contrast is genuinely hard to pick up from observation alone -- which is exactly why ear training helps.

What happens without training
  • ✗ "I think" sounds like "I sink" to native ears
  • ✗ "Thank you" sounds like "Sank you"
  • ✗ "Three" sounds like "See" or "Sree"
  • ✗ "Bath" rhymes with "bass" instead of "path"
  • ✗ "Mouth" sounds like "mouse" -- different animal
What changes with ear training
  • ✓ You start catching the tongue-position difference
  • ✓ The two sounds stop collapsing into one category
  • ✓ Production accuracy follows naturally
  • ✓ High-stakes moments ("think" vs "sink" in meetings) become stress-free
Spanish speakers

Latin American Spanish has no /θ/. Castilian Spanish does, but in a different phonemic distribution. The result is near-universal /s/ substitution among Spanish-speaking English learners.

Mandarin / Cantonese speakers

Neither Mandarin nor Cantonese has /θ/ or a similar dental fricative. Learners typically use /s/ or /t/ as substitutes, sometimes switching between the two mid-sentence.

Japanese speakers

Japanese lacks fricatives in this part of the mouth entirely. /θ/ is particularly challenging because the tongue-between-teeth gesture is unusual for Japanese phonology.

Production guide

How to produce /θ/ and /s/

/θ/voiceless th -- think, bath, mouth
  1. 1. Place the tip of your tongue lightly between your upper and lower front teeth.
  2. 2. Blow a steady stream of air over the tongue tip. No voice -- vocal cords are silent.
  3. 3. You should feel the air flowing over the tip and the edge of your tongue.
  4. 4. Hold the position for a second before saying a whole word. The tongue-between-teeth contact is the key.
Anchor words: think, thank, three, thin, thigh, thumb, bath, tooth, mouth, both, faith
/s/s -- sink, sun, class, pass
  1. 1. Tongue tip is behind the upper front teeth, not between them.
  2. 2. The sides of the tongue press against the upper side teeth, channeling air to the center.
  3. 3. Air is directed at the upper teeth and emerges with a sharper, higher-pitched hiss.
  4. 4. No voice -- just the high hiss of air hitting the tooth edge.
Anchor words: sink, sun, see, sit, six, sock, soup, school, pass, class, nice
The mirror trick

Hold a mirror in front of your mouth and say "think" slowly. You should see the tip of your tongue appear briefly between your teeth on the /θ/. Now say "sink" -- no tongue between the teeth. Once you can see the difference, you can hear it and feel it more reliably.

The "ssss to th" slide

Make a long /sssss/ sound. Now, while still making the sound, slowly push your tongue tip forward until it touches or passes through your teeth. You'll hear the sound change from /s/ to /θ/ mid-stream. That transition -- tongue behind teeth to tongue between teeth -- is exactly the distinction.

Click to hear

Minimal pairs: tap each word to hear it

English word pairs where the only difference is /θ/ vs /s/. Click each word to compare.

/θ/ voiceless th
/s/
to use the mind
↔
to go down in water
to express gratitude
↔
past tense of sink
upper leg
↔
a deep breath of weariness
not thick
↔
a moral wrong
the number 3
↔
to perceive with the eyes
More /θ/ words
thinkthankthighthumbthinpathbathmouthtoothbothfaiththreethrowthirtythursday
More /s/ words
sinksunseesitsetsocksoupsixsevenclasspassfaceniceboxschool
Common questions

Frequently asked

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/θ/ vs /s/ is just one English contrast

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