English Vogals - Basics of Pronunciation

Hey Maries and Johns,

One thing I never see teaching is the very basic orientation of how to know the correct pronunciations of vogals in English. Instead of portuguese, that aeiou is pronuncied the same way when embed in a word, in English they can vary. For example, in "adaption", the "a" is not "ei", but as portuguese "a". The same occurs with "e", when, i.e., "exam", "i", in interaction", "o" in "other" and "u" in "under". So, here's the question: how are grammar rules to learn correct pronunciations?

Great days everyone!