Humans have a unique ability (known in linguistics as Language Faculty) to process complex syntactic structures. Language Faculty is a subject of study by theoretical linguists.
After many years of intensive research in the field of theoretical linguistics, there has been significant progress in the deciphering of the general properties of human language. The recent expansion of research beyond English and other familiar European languages has enabled the refinement and verification of the central discoveries of theoretical linguistics.
People tried the idea of precprocessing with a lingutic parser that generates “parse tree”, but dealing with plain text directly leads to much better results. As the result, the progress achieved by theoretical linguistics in the study of the human language is not presently utilized in deep learning.