Oh my. You thought perhaps this was just a myth? How ever would we pronounce, rhythm?
We always bet for sexual favors so it’s a win-win situation but still… I hate to be wrong!! I can’t believe that I’ve gone 25 years without knowing this “rule” in the English language! Maybe I learned it and just blocked it out, I don’t know. Dammit! I hate to lose!!
I have often wondered why y is considered vowell “sometimes.” But I’ve always been on the other side of the issue. Why is it ever considered a consonant (in modern usage)? I will be more than happy to be informed of the errors of my ways. 
The master has already covered this.
Crwth is the Welsh word for the three- or six-stringed violin which is called in English a crouth or crowd.
I think it’s fair to say that w is a vowel in Welsh, but not in English.
From Merriam-Webster:
vow*el (noun)
[Middle English, from Middle French vouel, from Latin vocalis – more at VOCALIC]
First appeared 14th Century
1 : one of a class of speech sounds in the articulation of which the oral part of the breath channel is not blocked and is not constricted enough to cause audible friction; broadly : the one most prominent sound in a syllable
2 : a letter or other symbol representing a vowel – usu. used in English of a, e, i, o, u, and sometimes y
From Frannie, the elementary school teacher:
Y is a vowel in words such as cry, baby, * andhungry.*
Y is not a vowel in words such as *yarn, yellow, * and yours.
http://www.pbs.org/wgbh/lions/songs/sometimes_y.html
There, one can listen to a song entitled Sometimes Y by Paul Jacobs & Sarah Durkee. My favorite part is this:
*Five little vowels
A E I O U
When you got a couple consonants
Nothing else will do.
H-A-T hat
H-O-T hot
L-E-T let
L-I-T lit
I love them all a real lot
L-O-T lot.
Oh, and sometimes Y
Y don’t you cry.
You’re not a full-time vowel
But don’t throw in your towel
My little sometimes Y.*
(OK, I’ll shut up now. It’s just that this is such an adorable li’l song. I think I’ve had enough of summer vacation. ;))
With all due respect for Cecil, I’m not impressed by examples such as ‘cow’ where the ‘w’ is supposedly a vowel. If it needs to piggyback on another vowel (the ‘o’) to act as one itself, it may rate some special linguistic category (semivowel, dipthong), but it’s certainly a different critter from the other vowels, which are all capable of acting alone, as if they were a crazed assassin. 
Frannie said:
and I don’t ever want to argue with Frannie.
So can you explain a little bit the reasoning behind this? In each of these words it sounds to me like the y has a long e sound that (quickly) preceeds the coming vowell.
Rachelle
Wanna make a bet 
The teacher is always right. Just shush. You have me mumbling “y words” now. Geeeeeeeeeez (Truly though, I don’t hear any long e sound in *yarn, yellow, *and yours. You hear a long e?)
labradorian -
Sorry, my boss walked in and I was typing fast so I could post before he noticed what was on my screen.
I’ll paint a big red “L” on my forhead (for “Loser”) and sit in the corner now.
I don’t like TM’s explanation of “semi-vowels”. Y and W are semi-vowels not because they swing both ways, but because of their phonetic characteristics. These sounds are the elision between two vowels. It is the sounds (IPA [j] and [w], IIRC) that are semi-vowels, not the letters Y and W. In a language with an alphabet where J is used to represent the Y-sound, and there is no Y at all to represent a vowel, the J is still a semi-vowel.
So have I lost the bet or not. I said that Y isn’t a “real” vowel and he said it is considered a vowel when used in words such as cry, shy, try, etc. So technically, we’re both right. Call it a tie I guess.
Um, I don’t think it’s a tie; his argument is that y is “sometimes” considered a vowel, right? (It’s a good thing yours wasn’t a monetary wager. ;))
I think you are going to have to concede Rachelle.
The key thing to understand is that consonents and vowels are classifications of sounds. Letters are merely a means of representing those sounds.
While in English a letter may represent more than one sound it has just worked out that for 24 of the letters the represented sounds are all in one category or the other. Y and W have just developed in our language into representatives of sounds in both categories.
Y is a real vowel. Y is also a real consonant.
Light is a wave. Light is a particle.
See, it all makes sense.
Frannie–maybe I just talk funny…but without the y, “yarn” would be “arn.” How to describe the difference in the pronunciation between the two? I don’t know!! But for me to put a y there, I start out with an almost e-sound.
Do I get to stay after school now? (please?..)
I guess I can concede. I really hate to be wrong though. You’re right too Frannie, it’s a good thing we don’t bet for money. I’d be really upset if I had to give him money for this! Our way of betting makes it so neither one of us loses! I like that much better!
Written language alone does NOT count. If the “y” in a written word stands for a vowel sound in the spoken word, then it is a vowel. Thus, in “cry” since it stands for the /ai/ dipthong, it meets the criteria for a vowel. In the word “yes” it stands for the /j/ consonant sound, and so is a consonant. And it depends on your dialect as well. In all seriousness, “r” in many dialects qualifies as a vowel as well. It these cases indistinguishible from the German vowel “oe” as in “Schroedinger”. In many dialects in English, the first and third syllables of this name rhyme.
W is tricky, since it depends on your dialect whether or not it is sometimes a vowel. Does “sew” indistinguishable from “so” when spoken? If so, it is a vowel in your dialect. If not, then it is a consonant. “Cwm” is a Welsh word, and so is not often included in discussions of “w” as a vowel.