deep structure 
noun [mass noun]
(In transformational grammar) the underlying logical relationships of the elements of a phrase or sentence: rules of transformation change deep structure into surface structure...Contrasted with surface structure.
- The theory postulates that the two sentences have the same order in deep structure, but the question transformation changes the order to that in surface structure.
- Chomsky's initial proposals, in Syntactic Structures and Aspects, had distinguished between the surface structure of a sentence and the deep structure, from which the surface structure is derived by transformations.
- This would have to be the mythical deep structure of linguistics.