pronunciation - The + vowel letter

I've been told that when "the" is proceeded by a vowel sound, like "apple" or "hour", it's pronounced as "thee" and not as "thu".

But after listening to a couple of songs, I noticed that sometimes this "rule" is not followed. Take for example the two Katy Perry's songs, "Roar" and "The one that got away". In the first she sings "I got thee eye of thu tiger", but in the second she sings "Thu one that got away".

I don't know if it was sang this way to better suit the song melody (I understand nothing about those techniques), but I got confused. What's the correct pronunciation?

Thanks in advance.

Answer

You are correct, English speakers generally pronounce the with a long E (ði) before vowels and with a schwa (ðə) before consonants, just as we say an before vowels and a before consonants.

However, the rule follows pronunciation rather than spelling. While words like one and unicorn are spelled with initial vowels, the actual sounds are consonants (specifically, the labio-velar approximant [w] and the palatal approximant [j], often called semivowels). Therefore, these words use the articles for consonants:

A one-dollar note.
The (ðə) one-dollar note.

A unicorn.
The (ðə) unicorn.

Likewise, words like hour are spelled with initial consonants but actually sound as vowels, so they use the articles for vowels:

An hour.
The (ði) hour.

As others have mentioned, we don't follow the rule for the as rigorously as we do for a/an. There's some regional and personal variation, and we generally pronounce the with the long vowel (ði) when the word is stressed, regardless of the following sound.