Why do the vowels in unstressed syllables become schwas in English?

[Elsa]

Such as:
'a', as in about [əˈbaʊt]
'e', as in taken [ˈtʰeɪkən]
'i', as in pencil [ˈpʰɛnsəl]
'o', as in eloquent [ˈɛləkʰwənt]
'u', as in supply [səˈpʰlaɪ]
'y', as in sibyl [ˈsɪbəl]

How and when did this develop? Does it occur in any other languages?

[Smaug]

Yiddish and Hebrew influences. Schwa is Hebrew. Joking!

[Kale]

'v' in wheelbarrow
'w' in hexagon
'banana' in my butt

What are you trying to say?

[Elsa]

What are you trying to say?

The unstressed vowel in all the words in my original post becomes a schwa (ə).

[kkk77]

Maybe because a schwa is easier to pronounce?
English is a stress timed language, so unstressed syllables aren't much important.

In Portuguese there are two similar phenomena, some vowels are pronounce differently when they're unstressed:
A - ɐ:
Flaccid vs Flaccidity
Flácido /flasidu/ vs Flacidez /flɐsideʃ/


E - ɨ:
Cancels vs Cancelation
Cancela /kɐ̃sɛlɐ/ vs Cancelamento /kɐ̃sɨlɐmẽtu/

O - u:
Informs vs Information
Informa /ĩfɔɾmɐ/ vs Informação /ĩfuɾmɐsɐ̃w/

And, ɨ and u may not be pronounced in fast speech:
(Enemy) Inimigo: /inɨmigu/ -> /inmigu/
(Velocity) Velocidade: /vɨlusidadɨ/ -> /vlusidad/

[Comte Arnau]

Such as:
'a', as in about [əˈbaʊt]
'e', as in taken [ˈtʰeɪkən]
'i', as in pencil [ˈpʰɛnsəl]
'o', as in eloquent [ˈɛləkʰwənt]
'u', as in supply [səˈpʰlaɪ]
'y', as in sibyl [ˈsɪbəl]

How and when did this develop? Does it occur in any other languages?

In Catalan, it only happens with A and E in unstressed vowels. So to say Barcelona in the city's language, the 2 a's and the e all three are schwas: [bərsəˈɫonə].

But O and U are reduced to U here, and I is always I. It is certainly quite impressive that all vowels in English could literally become schwas.

[Kale]

The unstressed vowel in all the words in my original post becomes a schwa (ə).

Ok, I had never heard of a schwa before. That's just called a short 'u' in English. We do that for about, pencil, eloquent, it's supposed to be that way in supply, I've never heard the word sibyl, and we do not do that in the word taken.

[Smaug]

Maybe because a schwa is easier to pronounce?
English is a stress timed language, so unstressed syllables aren't much important.

In Portuguese there are two similar phenomena, some vowels are pronounce differently when they're unstressed:
A - ɐ:
Flaccid vs Flaccidity
Flácido /flasidu/ vs Flacidez /flɐsideʃ/


E - ɨ:
Cancels vs Cancelation
Cancela /kɐ̃sɛlɐ/ vs Cancelamento /kɐ̃sɨlɐmẽtu/

O - u:
Informs vs Information
Informa /ĩfɔɾmɐ/ vs Informação /ĩfuɾmɐsɐ̃w/

And, ɨ and u may not be pronounced in fast speech:
(Enemy) Inimigo: /inɨmigu/ -> /inmigu/
(Velocity) Velocidade: /vɨlusidadɨ/ -> /vlusidad/

Interesting, we totally lost this carachteristic in the dialects from Brazil.

[Elsa]

Ok, I had never heard of a schwa before. That's just called a short 'u' in English. We do that for about, pencil, eloquent, it's supposed to be that way in supply, I've never heard the word sibyl, and we do not do that in the word taken.

It is called a schwa in English, just it's a linguistic term that not everyone would know. An alternative term is "neutral vowel".

And it does occur in the word taken; Collins says it's pronounced ˈteɪkən.

[Comte Arnau]

It is called a schwa in English, just it's a linguistic term that not everyone would know. An alternative term is "neutral vowel".

And it does occur in the word taken; Collins says it's pronounced ˈteɪkən.

Actually I learnt about that name, schwa, when learning English. In Catalan we call it 'neutral vowel'.