 The theoretical problems which exist in the hypothesis relate to the role of input, the transfer of lexical categories, and the development of previous linguistic theories and research regarding L2 Acquisition research.The theoretical basis of the MTH has been contested by many researchers, which call into question the validity of the hypothesis.Vainikka & Young-Scholten themselves, the originators of the hypothesis, acknowledge that their theory is more "radical" than what is often seen in generative SLA academia.