for some reason?

[simonwai77]

Hi Sir
i Have been reading an American article.
And i always see phrases like
" i saw some guy ....."
" at some point"
or " i did it for some reason"

My question is that " guy , point and reason are all countable nouns here "
How come they are not plural
?
Would it be ok if i changed them all to " plural"
?
Thanks

[Alan]

'Some' preceding a singular count noun means 'a certain (X) that I shall not, or cannot, name'. It is used when the precise identity of a person or thing is either not known or not considered important.