In this short paper I argue that the statement "This sentence is ungrammatical" is logically paradoxical and very similar to one of the examples of the Liar paradox as well as other self-reference paradoxes. However it cannot be solved by the same methods that are used to solve the Liar paradox. I suggest a new solution that appeals to the tacit knowledge of a speaker-hearer. This paper is NOT about language and NOT an attempt to discover the role of logic in the faculty of language.