As in its mechanism, so in the essence of its modifications, the human
voice is a marvel of simplicity. If the mouth be opened naturally and
the tongue and lips be kept as much out of the way as in ordinary
breathing, and then the vocal cords be made to vibrate, the resulting
sound will be the vowel _a_ as in _father_. If now, starting from that
same position and with that same vowel sound, the tongue be gradually
raised the sound will be modified. Try it. The sound will pass through
other vowels. Near the middle position it will sound like _a_ in
_fate_; and when the tongue gets quite close to the roof of the mouth
without touching it the vowel will be the _e_ of _feet_. Others--such
as the _i_ of _it_--can be distinguished clearly.

Starting again from that same open position and with that same vowel
sound, _ah_, if the tongue be allowed to lie flat, but the lips be
gradually closed and at the same time rounded, the sound will pass
from _ah_ to the _o_ of _hope_, then on to the _oo_ of _troop_. The
_oa_ of _broad_ and other vowels can be distinguished at various
positions.

By moving lips and tongue at the same time an almost infinite variety
of vowel sounds can be made.

Producing Consonants. In order to produce consonant sounds the other
parts of the speaking apparatus are brought into operation. Everyone
of them has some function in the formation of some consonant by
interrupting or checking the breath. A student, by observing or
feeling the motions of his mouth can easily instruct himself in the
importance of each part if he will carefully pronounce a few times all
the various consonant sounds of the language.