Silent i and u: The phonetics of vowel devoicing (無声化)

Mental Model: The Whispered High Vowels

When learners hear native Japanese speakers say です or ます, they often wonder: “Why don't I hear the ‘u’ sound at the end?”

This is not lazy slang or careless articulation—it is an ironclad, automatic phonetic rule of the Tokyo standard dialect known as vowel devoicing (無声化(むせいか) (devoicing)):

• In Japanese, the high close vowels “i” and “u” require very little jaw movement and mouth aperture.
• When one of these weak vowels gets sandwiched between two voiceless consonants (sounds made without vibrating your vocal cords), the vocal folds don't bother switching on for a split second!
• Instead, the mouth forms the vowel shape while airflow passes through as a silent whisper.

The Voiceless Consonant Club

The consonants that trigger devoicing are completely voiceless (put your fingers on your throat: say “sss” and notice zero buzzing; say “zzz” and feel the strong buzz):

• The Triggers: K, S, SH, T, CH, H, and P.
• High Vowels: Only い /i/ and う /u/.

The Two Major Environments for Devoicing

Devoicing occurs predictably in two distinct positions:

• 1. Sentence-Final After a Voiceless Consonant: At the end of an utterance, the final /u/ of polite verbs and the copula drops its vocal cord vibration:
• 学生です。(がくせいです。) → Pronounced gakusei des(u).
• 食べます。(たべます。) → Pronounced tabemas(u).
• 〜でした → Pronounced desh(i)ta.
• 2. Internal Syllables Sandwiched Between Voiceless Consonants: Inside ordinary words, the vowel is whispered between the two consonant sounds:
• 好き(すき) (S + u + K) → Pronounced s(u)ki (“like”).
• 靴下(くつした) (K + u, T + su, SH + i) → Pronounced k(u)ts(u)sh(i)ta (“socks”).
• 明日(あした) (SH + i + T) → Pronounced ash(i)ta (“tomorrow”).
• 人(ひと) (H + i + T) → Pronounced h(i)to (“person”).

The Crucial Secret: Pitch Accent is Still Preserved!

Even though the vowel loses its vocal vibration, Japanese speakers still mentally count the syllable as a full mora, and the pitch accent contour remains intact. Never delete the timing beat—simply whisper the vowel without buzzing your throat!