If "think" sounds like "sink," you're missing the th — here are its two sounds

You've memorized thousands of words, but th still gives you away.

Think comes out as sink, this as zis, and three turns into tree.

Good news: th only has two sounds, and telling them apart takes one finger.

Sound 1: /θ/ — voiceless (no vibration)

Rest the tip of your tongue lightly against your upper teeth, or push it out between your teeth, and let the air leak through. Your vocal cords stay off. It's not an s, and it's not a t.

• think /θɪŋk/, thank /θæŋk/, three /θriː/, mouth /maʊθ/, bath /bɑːθ/

think is not sink. For s, the tongue stays back behind the teeth; for /θ/, the tongue tip must come forward and touch the teeth.

Sound 2: /ð/ — voiced (vocal cords vibrate)

Exactly the same mouth position as /θ/ — tongue tip on or between the teeth. The only difference: your vocal cords buzz. It's not a z, and it's not a d.

• this /ðɪs/, that /ðæt/, mother /ˈmʌðə/, brother /ˈbrʌðə/, breathe /briːð/

this is not zis or dis. The tongue still touches the teeth — don't pull it back.

A trick you don't have to memorize: put a finger on your throat and make the sound. Buzzing → voiced /ð/ (this, mother). No buzz, just airflow → voiceless /θ/ (think, three). The tongue is in the same place both times — the only question is whether you turn your voice on.

The three pairs people miss most: think ≠ sink, three ≠ tree, breathe ≠ breeze. The moment your tongue tip dares to touch your teeth, they all fall into place.

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