How an Open Passage Becomes a Vowel
When you say a vowel, air from the lungs can travel through the mouth without being stopped by a full closure. The vocal folds usually vibrate as that air passes them, creating a voiced sound. The mouth then reshapes the sound rather than blocking it.
The tongue and lips change the size and shape of the spaces inside the vocal tract—the passage from the vocal folds to the lips. These changes make some sound frequencies stronger than others, much as the shape of a resonant chamber colors a steady tone. The resulting peaks in the sound are called formants; their pattern helps listeners distinguish one vowel from another.
Small Movements, Different Sounds
Move the tongue forward or backward, raise or lower it, or round the lips, and the vocal tract’s resonances shift. That is why the vowels in “heed,” “head,” and “had” sound different even though each is made without a consonant-like blockage. The tongue does not need to touch the roof of the mouth: a narrow opening can still let air flow continuously.
“Open” does not mean the mouth is held wide or that every vowel uses an identical passage. It means the airflow is not fully shut off at the main point of articulation. The jaw, tongue, and lips can still constrict or redirect the passage, and those precise shapes give vowels their character.
This is also why a tiny change in tongue position can make a noticeable difference: it alters the vocal tract’s resonances, changing the sound even while the air keeps moving.
