@Naveen , A Language is called Inherently Ambiguous if all the grammars which generates this language that all are ambiguous ie. if no unambiguous grammar exist for a language then it is called Inherently Ambiguous... "Whether a CFL is inherently ambiguous or not ?" This problem is undecidable .. Bcoz there is no algo for it...But I don't know it is undecidable for csl , recursive , recursive enumerable , non-recursive enumerable languages or not ?