Each vowel letter of English uses three or four different vowel sounds, but there is something unique about the letter “I” — it shares its sounds with the letter “Y”. They are sort of like “twins”. Whenever the letter “Y” is acting as a vowel, it uses the same sounds as “I”.
There are three basic sounds for the English letter “I”: Long-I, Long-I-2 (old-style), and Short-i.
Long-I is the normal Long-vowel sound for “I”, because it is the same as the name of the letter “I”. Some common words with this sound are: like / write / time / line / right / kind / while / life / side / five / ice / sign / child / tie / item / my / why / type / style / rhyme / cycle / deny / apply / rely.
The second Long sound that the letter “I” (or “Y”) uses is the “old style” Long-I — it is the sound that the letter “I” used hundreds of years ago, before the English vowels made a shift. A few words with the letter “I” retained the old sound, which is the same as the Long-E sound today. Here are some examples: ski / chic / police / machine / tangerine / mobile / souvenir / antique / magazine / unique / many / only / funny / baby / lady / very.
Short-i is pronounced in the front upper part of the mouth, and it is very important to relax the tongue to avoid confusion with the Long-E sound (see This or These). There are quite a few frequently used words with the Short-i sound, so it is important to learn to relax the tongue well. Some words are: with / six / which / if / give / thing / think / big / list / inch / spring / quick / sing / myth / gyp / gym / cyst / lynx / system / rhythm / symbol.
In addition to the basic Long and Short-vowel sounds, any vowel letter can also use the schwa sound. This happens in weak (unstressed) syllables, especially in a syllable that is adjacent to the strongest syllable of a word. In the following words, the letter “I” (or “Y”) is in an unstressed syllable: pencil / decimal / practice / office / chemical / flexible / dactyl.
Some tricky cases
The following words can be confusing because they are homographs.
L-I-V-E: this word could be a verb or an adjective, and they are pronounced differently. When it is a verb, it has a Short-i: “live”. When it is an adjective, it is pronounced with a Long-I: “live”.
W-I-N-D: this word could be a noun or a verb. As a noun, it has a Short-i: “wind”. As a verb, it has a Long-I: “wind”.
So remember, when you see the letter “I”, it will be pronounced with one of the four choices: Long-I, Long-I-2, Short-i, or Schwa. It is very unusual for an “I” to use some other sound.