Real clips from the app. Turn your sound on.
TH is a soft, flat breath. S is a sharp hiss.
This can be trained
Hearing these sounds apart is a skill, not a talent. Most research on high variability phonetic training (HVPT) has used other sounds, such as L and R or vowels, and very little has looked at TH and S. But the method itself is well tested. Ron Thomson's 2018 review of 32 HVPT studies found strong evidence that it works and that the gains last.
Studies: Thomson 2018
Easy
8 pairsShort, common words. For consonants, the sound is at the start of the word.
- think · sinkWhere the sound is: Start of the word
- thick · sickWhere the sound is: Start of the word
- thing · singWhere the sound is: Start of the word
- thank · sankWhere the sound is: Start of the word
- thin · sinWhere the sound is: Start of the word
- theme · seemWhere the sound is: Start of the word
- thumb · sumWhere the sound is: Start of the word
- thought · soughtWhere the sound is: Start of the word
Medium
5 pairsClusters, word endings or less common words.
- path · passWhere the sound is: End of the word
- mouth · mouseWhere the sound is: End of the word
- faith · faceWhere the sound is: End of the word
- math · massWhere the sound is: End of the word
- myth · missWhere the sound is: End of the word
Hard
2 pairsMiddle of the word and longer words.
- worth · worseWhere the sound is: End of the word
- tenth · tenseWhere the sound is: End of the word
How to hear the difference between TH and S
Listen for the hiss. S is a strong, sharp hiss. The TH in think is a soft, flat breath, much quieter, with no edge. The skill is catching that difference in every voice.
How TH and S are made
For TH, your tongue tip rests lightly against the back of your upper front teeth, or just between them. The tongue stays flat, and air spreads out over it, so you hear a quiet, soft breath.
For S, the tongue tip comes up near the ridge behind your upper teeth, and a narrow groove in the tongue aims a fast stream of air at your teeth. That makes the high, sharp hiss. Try a long S, then slide your tongue tip forward to your teeth. The hiss goes soft and flat, and that's TH.
This page covers the TH in think. The TH in this uses your voice and is a different sound.
Why do TH and S sound the same to Japanese speakers?
Your ear is tuned to your first language. Japanese has no TH, so a Japanese ear files it under the closest sound it has, S. Thank you is borrowed as "sankyū", and in katakana think and sink are spelled the same, as are thumb and sum.
Korean and Chinese don't have this TH either, and learners often say it as S, sometimes as F or T. Your ear picks up both sounds. What needs training is how your brain sorts them.
What to listen for
At the start of a word, as in think and sink, ask one thing: does it begin with a hiss? TH is so quiet that you may barely hear it before the vowel. No hiss means TH.
Word endings are harder. In pass and mouse, the S hisses right to the end. In path and mouth, the TH just fades out on a breath. After another consonant, as in worth and worse or tenth and tense, the sound is even shorter, so listen to the very end.
If a TH sounds a bit like F, that's normal. Both are quiet, and some native speakers, in London for example, say "fink" for think. Quiet means TH, not S.
How to practice hearing TH and S
Use many voices, not one. Every speaker makes TH and S a little differently. With one voice, you mostly learn that voice. With many, you learn the sound.
Check each answer right away, while the word is still in your ear. Keep sessions short and do them often. Start with pairs where the sound comes first, like thin and sin, then move to word endings like path and pass. How much you improve, and how fast, varies from person to person.
How the app uses this list
Each session plays 20 words from your current level, each one spoken by a different voice. Score 17/20 or better and the next level opens.
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