Why is the phrase "personal reasons" is preferred to "personal reason"?
Example: I'm on leave due to personal reasons.
I hardly have seen anyone saying "I'm on leave due to a personal reason."
Are there any differences? Isn't it grammatically correct to use the phrase in singular?
"Personal reasons" is intentionally vague, and would be understood that way. It would not usually prompt a question as to what the reasons are, though hearers might speculate. It might be used even if there is only one specific reason.
Saying "a personal reason" is less vague, implying something very specific. It would almost seem to invite the question "What is that reason?"
Saying "personal reasons" practically means "please don't ask me for any further details." I don't hear "personal reason" very often.
Because when someone uses that phrase there is rarely just one single reason behind their decision & even if there was, saying "personal reason" would seem "suspiciously specific" even though the reason is not stated & would pique others' curiosity & invite speculation & assumptions.
It isn't a issue of grammatical correctness but social correctness.
When someone says "personal reasons" it simply means they do not wish to go into specific details, that is all. It doesn't even mean something negative happened, the reason or reasons may be perfectly normal & understandable, (or even very boring) but the person may simply not wish to repeat them over & over to different people, (especially if the explanation is long & boring) so they might simply say "personal reasons" to save time (and attention spans).
