The cords [...] are capable of at least three distinct types of movement, each of which is of the greatest importance for speech. They may be drawn towards or away from each other, they may vibrate like reeds or strings, and they may become lax or tense in the direction of their length.
- Sapir (1921), a pag.47

The unimpeded breath takes on a particular color [...] in accordance with the varying shape of the oral resonance chamber [...] As the tongue is raised or lowered, retracted or brought forward, held tense or lax, and as the lips are pursed ('rounded') in varying degree or allowed to keep their position of rest, a large number of distinct qualities result.
- Sapir (1921), a pag.50