Question

Why is 'an ' used in John is an honest man? why not 'a '?

Answer 1

An is used before honest becoz when we pronounce honest h is silent and it sounds like onset thus the sound comes of o and not h. O being a vowel we use an

Answer 2

well we know that the article an when there r vowels and article a where there r consonants but we also do u article for words with vowel sound hence in honest there is a sound of "o" which is vowel hence we say
JOHN IS AN HONEST BOY
hope this helped u :-)