The definition of language has been suggested as a transformer between the two equivalent representations of information, the Text, i.e., the surface textual representation, and the Meaning, i.e., the deep semantic representation. This transformation is ambiguous in both directions: a homonymous Text corresponds to several different Meanings, and several synonymous Texts correspond to the same Meaning.
The description of the transformation process is greatly simplified by introducing intermediate levels of information representation, of which the main are morphologic and syntactic. At each level, some of the problems arising from synonymy and homonymy can be solved.
The general definitions of linguistic sign in Meaning Û Text Theory and in Head-driven Phrase Structure Grammar turned out to be in essence equivalent.