Native speakers say sugar as SHUG-er and measure as MEZH-er, yet the spelling starts with a plain S. This is not random. The letter U hiding after S is doing the work.
When S meets a U that carries a /j/ (a tiny "y") sound, the S slides back in the mouth and becomes /ʃ/ (sh) or /ʒ/ (zh). Linguists call this palatalization, and it runs through dozens of everyday words.
The Rule
When SU comes before a vowel and the U carries a /juː/ or /u/ glide, S becomes /ʃ/ in unvoiced words (sugar, sure, censure, pressure, issue, tissue) and /ʒ/ in voiced ones (measure, pleasure, treasure, casual, usual, leisure, vision-type endings).
See the Pattern in Action
| Spelling | Sound | Example |
|---|---|---|
| SU (voiceless) | /ʃ/ (sh) | sugar, sure, censure |
| SSU | /ʃ/ (sh) | issue, tissue, pressure |
| SU (voiced) | /ʒ/ (zh) | measure, pleasure, casual |
| SU + consonant | /s/ + /uː/ (regular) | super, sudden, suit |
Words to Practice
Common Exceptions
SU stays a normal /s/ + /uː/ when U is followed by a consonant or opens a stressed, un-glided syllable: super /ˈsuːpər/, sudden /ˈsʌdən/, suit /suːt/, sum /sʌm/, suffer /ˈsʌfər/. Also note sure and sugar are the two classic word-initial exceptions where /ʃ/ appears at the very start.
Quick Tips to Remember
Test with a slow, relaxed voice: if a /j/ ("yoo") wants to sneak in after the S, the S usually turns to SH or ZH. Group voiced words (measure, pleasure, treasure) together and unvoiced words (pressure, tissue, issue) together. Then practice your pronunciation out loud.