A description of relationship of the deep and surface structures in a grammar. Some linguists have posited that when the surface structures become too different from the deep structure (in other words, when the degree of exceptionality reaches a currently undefined threshold), speakers will reanalyze the grammatical meaning, or reform the grammar to keep the surface structures more like the deep structures. A high degree of exceptionality may thus be an impetus for syntactic change.
Persons who demonstrate learning and behavior disorders, speech and language disorders, sensory disorders, physical, and other health disorders are identified for service due to their exceptionality.