阿 sometimes pronounced 'a' sometimes pronounced 'e'.
I've noticed specific instances for both.
Are there any rules as to how to pronounce 阿 in different circumstances/contexts?
Yes, there are rules - it is not irregular at all.
The two different pronunciations of 阿 actually reflect different usages. The original Old Chinese pronunciation of ē is for using the character as a verb or noun, which is what the character 阿 originally meant. In contrast, the later pronunciation of ā emerged as a particle with completely different meanings.
Unfortunately most people have became unfamiliar with the older usage, so that the ē form is usually only seen in set phrases (成語).
阿 ē
verb, meaning:
- to pander to
- to (unjustly) side with (someone in a dispute)
noun (archaic), meaning:
- a hill
- a (geographical) twist/turn
- a building
A surname
阿 ā
prefix for names or familial titles, originally meaningless but can carry connotations of:
- familiarity
- endearment
particle (archaic, superseded by 啊) indicating:
- surprise
- doubt
As the above shows, the two different pronunciations do not overlap in their usage.
'e' is the older pronunciation and is used to reflect the older pronunciation in some particular words (usually more formal words), such as 阿胶 (ē jiāo, some animal gelatin), 阿房宫(ē páng gōng -- notice that 房 is pronounced páng instead of fáng), 阿谀奉承.
'a' is the modern and default pronunciation, used in translation of foreign names (e.g., Algebria - 阿尔及利亚) as well as some colloquial/informal addresses/names to express familiarity (e.g., 阿爸, 阿伯, 阿花)
You may treat 'e' as an irregular pronunciation and memorize irregular words.
