A Dennis,
I notice in Foclóir Póca, that when "ceart" is used as a noun, there's usually an "i" before it. For example, from FP, "níl a fhios agam i gceart" (I don't really know). But when used as an adjective, there isn't an "i" before "ceart." For example, again from FP, "nil an fear sin ceart" (that man is not right in the head).
I just thought I'd provide the above for review and comment, and I don't mean to sound as though this is the correct approach that FP takes.
I did get a kick out of the definition of "níl an fear sin ceart" as being "not right in the head." I would have thought it to mean "that man is not right" and that it would have nothing to do with his state of mind. Perhaps then there is a difference between the two forms, that is, for example:
Níl an ceart aige: He is not right
Níl sé ceart: He is not right in the head.
Just thinking. (Hmmm...I smell wood burning.
)