What exactly is a long vowel sound?

Question

I am having a hard time grasping the definition of the term 'long vowel sounds', a long vowel sound is defined as a sound with the same pronunciation as its letter. The long vowel a, e, i, o sounds all follow this definition, while the long vowel u sound doesn't. There are two long vowel sounds for letter u, while there is actually only one pronunciation for the letter u.

Answer 1

This is a notable lie to children.

Native speakers, before they learn to read, don't think about phonemes and so on. They just know words. They know "Cat" and "Kate", and "Sit" and "Sight".

When teachers of very young children are teaching them to read, they might teach "The letter "a" has two sounds a short sound /a/ and a long sound /ei/. The letter "i" has two sounds, a short sound /i/ and a long sound /ai/. The letter "e" has two sounds /e/ and /i:/". So the word "Cat" has a short "a" and "Kate" has a long "a".

These pairs of sounds developed from the great vowel shift in English, in which the long /a:/ sound changed to a dipthong /ei/ and so on. (its more complex than that but you can read the details yourself)

Don't confuse these with what the linguist calls long and short vowels. In English, vowel length isn't particularly important. The teacher is lying to teach the children how to read simple words.

An English second language learner needs to learn the sounds of the words, so this idea of "long" and "short" vowel sounds isn't particularly useful. So don't worry about it. It is not something you need to know to speak and read English well.

Answer 2

You're correct that, except for U, vowels are named after their long sounds. With some of the vowels we need to add an extra letter to indicate the long version

A long - Kate, hate, mate
A short - cat, hat, mat

E long - feet, meet
E short - get, met

This also works for I and O
Mitt mite
hop hope etc

U has a simple short version, in a similar pattern to the others - tub, cub, rub etc, where an accent variation still remains internally consistent.

On the other hand, though called 'yoo', has two long pronunciations - basically with or without the Y sound at the head [some might call it an E sound]. There's the simple 'oo', or the diphthong 'yoo' or 'eoo'. The indicators for this are much weaker, and can change quite drastically between British & US English.

In British English, You Tube is yoo tyoob [or even chyoob/chewb].
US English often drops the 'y' sound in these, giving Yoo Toob.
Similarly with Tuesday - toosday [US] vs tyoosday or chewsday [UK]. [I won't go into the British dropping of T down to CH or the US T to D drop.]

So, though there are some words we agree on; ruby [roobi], lunar [loona], frugal [froogəl] , there are many we disagree; tube [as mentioned] tune, altitude, attitude, produce. In UK English these have the 'yoo' sound, in US the 'oo' (there are variations even inside these large accent groups, not everybody pronounces each of these words according to that general rule.)

I can't think of any way to be able to know these just by reading for the first time. There is no hard and fast rule that I'm aware of. You just have to learn which is which for the specific accent you are trying to emulate.

To elongate our earlier short examples, we also see the inconsistency - tube, cube, rube. [toob or tyoob, cyoob & roob.]

^{Whilst looking for a more comprehensive online guide to this, I came across https://literacylearn.com/215-long-u-words/ at which point I realised just how many of those pronunciations are not trans-Atlantic, or even consistent between different accents either side of the pond.}