Diphthongs OI OY Sounds
A diphthong is two vowel sounds glued together in one syllable. OI (coin, point) and OY (boy, toy) both make the same sliding oy sound. Your mouth slides from o to i without pausing. Similar diphthongs include OU (out) and OW (cow). Diphthongs are vowel teams that make a unique combined sound.
The Core Idea
OI vs OY rule: OI in the middle of words (COIN, JOINT, VOICE). OY at the end of words (BOY, TOY, JOY). Exceptions exist but this pattern holds ~85% of the time. Same sound, different spellings — just remember the position.
Examples
OI: coin, boil, point, joint, voice, soil, spoil. OY: boy, toy, joy, employ, enjoy, destroy. Rhyme: boy and coin both have the same sliding vowel sound. Try saying them with exaggerated mouth movement — feel the slide?
Where does OY usually appear?
Going Deeper
Diphthongs are why English spelling can feel weird. Phoenician alphabets had mostly 1 sound per letter. English inherited vowel teams from Old English, French, Norse. Today the OI/OY split is a leftover — and knowing it makes you a confident speller.
OI/OY Sort
Write a Sentence
Do OI and OY sound the same?
Which ends with OY?
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