Who's asking: Larry Willis, St. Louis, MO
Every first-grader knows -- or should know -- that English vowels are a,e,i,o,u and sometimes y. Conscientious English teachers may add, "and sometimes y and w." Larry wants to know when "w" is a vowel.
Although Welsh uses "w" as a vowel in words such as cwm (which means "valley," and is transliterated into English as "coombe"), English uses w as a vowel only in diphthongs. "W" acts as a vowel in combination with "e" and "o," in words such as new and how. It gives the letters e and o sounds those letters would never have, standing alone, and is phonetically equivalent to the true vowel "u." (It may also stand in for the silent "e," in words such as tow and show.)
In these cases, w's role as a vowel is a linguistic detail, and not something first-graders really need to worry about.
W is an interesting letter. Latin didn't have it, and it's still rare to find it in any Romance language; English adopted it from Germanic languages sometime in the Middle Ages, and it doesn't show up in manuscripts until after the Norman Conquest of 1066. What, I wonder, did we call wiggly worms before then?