Is the 'w' in 'cow' a vowel or a consonant? [duplicate]

Is the w in cow a vowel or a consonant?
Assuming it is considered a vowel, would it likewise be so in how?

I learned that the vowels are "a, e, i, o, u, and sometimes y."

If w can be a vowel, what other letters can be vowels?
What is the definition of a vowel?

By the way, I know w can be a vowel, for example in the word cwm, described in the OED as:

A valley; in Physical Geogr., a bowl-shaped hollow partly enclosed by steep walls lying at the head of a valley or on a mountain slope and formed originally by a glacier; a cirque.

(See Semivowels in English and When is Y a vowel? for relevant info)

The sounds represented by the letter 'w' in English spelling are somewhat intermediate between consonants and vowels. Sometimes it is closer to a consonant (namely a semivowel or glide because even though 'w' doesn't result in a substantive occlusion in the airstream, there is a restriction of airflow as with the similar glide y. This occurs when the sound (with corresponding letter) appears at the beginning or middle of a word or syllable.

But the letter can also represent a sound that is closer to a vowel when it is part of a diphthong (a double vowel or a vowel followed by a glide, like in the word 'brown').

Which is all to say that the dichotomy of consonant/vowel, while very useful, does not capture the entire complexity of articulation; there are more overlapping categories between a stop (like 'p') and a pure vowel (like 'a').

As to 'cwm', it is a borrowing like the 'll' in 'Lloyd' that represents a non-native (to English) sound and the non-native spelling.

So to summarize for you explicit questions:

• 'w' in 'cow' is a glide (which is considered a consonant (but a sonorant which is closer to a vowel))
• yes, it is the same as in 'how'.
• if 'w' is vowel-like, 'y' is similarly vowel-like.
• a vowel is a sound produced by "no build-up of air pressure at any point above the glottis".

The original rhyme went like so:

A, e, i, o, and u — and sometimes y and w.

It helped students memorize the five vowels and the two dependents. The original Greek also had five vowels and two dependents: α (alpha), ε (epsilon) and η (eta), ι (iota), ο (omicron) and ω (omega), and υ (upsilon) — here listed out of chronological order in the Greek alphabet to show the similarity with the English rhyme.

W is also a vowel in words like fallow, mellow, and hollow where it is silent, similar to the e in tube. And, of course, that rule follows for the y in turkey, monkey, and their ilk.

I don't have any research per se; I'm just really old and remember my elementary teachers. Sadly, you're right, students aren't taught anymore where their language came from and why grammar or spelling rules exist.

Hope that helps.