Hmm, if anything that link seems to imply it's invalid - plus it's Quora, not exactly a high quality reference.
The rule is "an" is used in front of a word that starts with a vowel sound[1]. "An hour" is correct because the "h" is silent. All modern (native) English dialects pronounce the "h" in history, ergo "an history" is incorrect grammar.
The rule is "an" is used in front of a word that starts with a vowel sound[1]. "An hour" is correct because the "h" is silent. All modern (native) English dialects pronounce the "h" in history, ergo "an history" is incorrect grammar.
[1] https://en.wikipedia.org/wiki/English_articles#Distinction_b...