The use of the term "deep structure" here has the same meaning
as used by Noam Chomsky.
Chomsky distinguishes the "surface structure" of sentences, which is the form of a language we habitually use, from the "deep structure" which underlies and underpins the true semantic content of the sentence.
The surface structure is by definition revealed to us whereas deep structure is subliminal and its form can only be accessed through theoretical investigation.
Although we do not see and are not directly conscious of deep structure it is the base upon which linguistic communication is built.
The surface structure of every language is different whereas the deep structure
is by definition always the same.
The concept of deep structure is thus equivalent to that of a "universal grammar".
A test of the adequacy of a theory of deep structure is that it works
for every known language.
The deep structure for Chomsky took
the form of a "transformational grammar" which he invented.
In this essay an entirely different new theory of deep structure is put forward.
An essential idea behind this new theory is that deep structure must reveal something fundamental to human thought.
The theory has been exhaustively tested on actual sentences to ensure that it is robust enough to be able to provide a deep structure for every possible sentence. Examples of this research are given at the end of the book