An interesting marker is when the letter R follows a vowel. Unlike most languages where the vowels have just one or, at the most, two sounds, English vowels have an extraordinary variety of sounds. This makes for a colorful and expressive language for those who use it skillfully, but a helluva problem for the learner.
The A. When an R follows an A, as in “part,” the vowel sound will change, but it will not become short, as in “pat.” Nor will it become long, as in “pate.” It has a special sound as in “cart,” “dart,” “mart,” and “start.”
However, when AR follows a W or a QU. we get a completely different sound. Pronounce “war,” “warm,” and “quarter” and you’ll hear the difference.
The O. An O before an R is similar. “Port” differs from both “pot” and “note” and “poor,” although it does sound a bit like “door.” Pronounce “north,” “born,” and “mortal.”
Again, when OR follows a W, we get a different sound. Pronounce “word,” “world,” “worm,” and “worship.”
The E. When an E is followed by an R, it is neither a short nor a long vowel, but something special and rather like UR. Pronounce “her,” “clerk,” “mercy,” and “expert.”
The I. Now listen to the sound produced when an I is followed by an R. It is almost the same as ER, above: “girl,” “bird,” “first,” “third.”
The U. When an R follows a U, it produces a sound unlike the U in “uncle” or “cute.” Pronounce “turkey,” “murder,” “burn,” and “fur,” and you’ll hear a sound very much like the E, I, and WO before R..
The Y. As if it wants to be contrary, the vowel Y before an R has three different sounds, as in “pyrite,” “pyramid,” and “myrrh.” But notice that “myrrh” and “myrtle” have the same vowel sound as E, I, WO, and U before R.
The marker R warns us of a changed vowel sound, even though five of the eight examples we have just looked at sound very much alike: “word,” “girl,” “burn,” “myrtle,” and “her.”
Two of the other examples have a similar vowel sound: “warm” and “born.”
There are of course a few exceptions and anomalies, but these pronunciations of R with vowels are clearly the pattern. R is one example of why so many people say that it is time to clean up English spelling. Pity the thousands of students (both domestic and foreign) trying to learn English who have to sound out how to pronounce words with R and a vowel.