Other or another

i know this sentence is right: There could be other reasons why he does not write.

but i want to know something, when i’m talking in singular:: there could be another reason or there could be other reason::::: are both of them right?

and when can i use::: another, another one, other one… when it is singular i always say … another person or another one instead of other one … i hope your help

There could be another reason - one additional reason, different than the one we know)
*There could be other reason - I don’t find this correct
(…)the other reason (is this…) - the only other reason, different than the one we know)
There could be other reasons - several possible reasons)
There could be others - same as above

Basic suggestion: use singular after “another” and plural after “other”, unless you’re point out a certain object in which case you should add “the”.

what you mean is: SHE IS THE OTHER GIRL I TOLD YOU AND MARY IS ANOTHER ONE… my question is more about the singular form, if these sentences are right i got it if they are not… explain that for me again please— thanks a lot…

there could be another reason—correct

there could be other reason—incorrect

Here’s a rule of thumb you can use. Think of “another” as “one other” (or “an other,” the form that existed in English up until the 16th century). “Reason” is a count noun, so it requires an article. Hence, you must say either “there could be one other reason,” or “there could be another reason” (which you did), but never *“there could be other reason.”

waoo— thanks a lot Mr. Astamoore, I finally got it --------- very good explanation… it’s very clear… more questions are coming